An experiment was conducted in two stages. The first stage was to investigate the effect of soaking duration on the proximate composition and anti-nutritional factors (ANFs) of soybean (Glycine max (L.) Merril), while the second stage was to evaluate the performance of Friesian x Bunaji calves fed different ratios of soy:cow milk. In stage one of the experiment, soybean was sourced, cleaned and divided into five groups (intended for the experimental treatments). The first group was the control (unsoaked soybean), while the other groups were soaked in clean water for 12, 24, 48 and 72 hours, respectively. The water was changed twice after every 24 hours of soaking. Thereafter, the soybean was rinsed, sun-dried for 8 days, milled, sieved and then taken to the laboratory for analyses. Results of the proximate composition showed that unsoaked soybean xix (control) had 40.28% crude protein, 14.11% fat and metabolizable energy of 3459.50 kcal/kg DM. While soybean soaked for 72 hours had 44.37% CP, 29.55% fat and ME value 5514.57 kcal/kg DM. Soaking improved the chemical composition as well as reduced the levels of anti-nutritional factors in the soybean especially at 72 hours duration. The crude protein content of the different ratios of soy:cow milk diets increased with increase levels of soymilk and varies from 3.29% in 0:100 to 5.23% in the diet containing 75:25 ratio of soy:cow milk. The total solid, fat, solid-not-fat and ash contents also followed similar pattern. In the second experiment, a growth trial was carried out to evaluate the feeding value of the best soaking duration (72hrs) in combination with cow milk at a ratio of 0:100 (control), 25:75, 50:50 and 75:25 soy:cow milk, respectively in the diets of Friesian x Bunaji calves. Sixteen calves with average body weight of 34.8�0.7kg were randomly assigned to four dietary treatments with 4 calves per treatment in a Completely Randomized Design. Results from the growth trial showed that there was no significant difference (P>0.05) in average total feed intake among calves fed the different ratios of soy:cow milk. Calves fed diet containing 25:75 ratio of soy:cow milk had the lowest total feed intake (409.64 kg), average daily feed intake (4.18 kg/day) and better total weight gain (74.25 kg), average daily weight gain (0.76 kg/day) and feed conversion ratio (5.52) as against (416.29 kg), (4.25 kg/day), (66.00 kg), (0.67 kg/day) and (6.31), respectively in calves fed cow milk alone (control). Inclusion of soymilk at different ratios had positive influence on some linear body measurements (body length, height at withers and heart girth) of calves. The blood parameters measured were within the normal range for healthy calves, indicating that soaking of soybean in water for 72 hours had significantly reduced the levels of ANFs in the soymilk fed to calves. White blood cells and glucose were within the normal range (4 - 12x109/l) and (40 - 100mg/dl), respectively. Feeding different ratios of soy:cow milk had positive influence on rumen metabolites (rumen fluid temperature, pH, NH3-N and TVFA) with 75:25 ratio of soy:cow milk raton having the highest concentration of RAN (13.84 mg/100ml). Sampling time significantly (P<0.05) influenced rumen temperature, pH, NH3-N and TVFA concentrations. Digestibility of DM, OM, CP, NDF and ADF xx were significantly (P<0.05) influenced by the inclusion of soymilk at different ratios. However, calves fed 25:75 and 75:25 ratios of soy:cow milk had better nutrient digestibility and nitrogen balance, respectively. The cost of cow milk per litre (N98.00) was about 3 times higher than soymilk (N33). Calves fed 25 and 50% soymilk had better feed cost per kg weight gain N496.10 and N469.67, respectively. Calves fed 75:25 ratio of soy:cow milk had the least total cost of feed consumed (N 30489.00). Indicating that feeding cow milk alone to calves was very expensive compared with feeding soy:cow milk at 75:25 ratio. It was concluded that soaking of soybean in water for 72 hours reduced the levels of ANFs and improved the nutritive value. Feeding 25:75 soy:cow milk improved live weight gain by 0.76 kg/day as against 0.67kg/day in calves fed cow milk alone. From an economic standpoint, feeding soy:cow milk at a ratio of 75:25 reduced the cost of feeding by (24.16%) as compared with feeding cow milk alone. Therefore, soaking of soybean in water for 72 hours was recommended for good result. And feeding calves with 25:75 ratio of soy:cow milk is recommended for better performance and feed conversion than feeding cow milk alone