Improvement of groundnut (Arachis hypogaea L.) is constrained by its narrow genetic base. Studies were conducted to compare the sensitivity of groundnut genotypes to different doses of thermal neutron irradiation, to determine the effective dose for the induction of variability among the genotypes and to evaluate the variability for farmer preferred traits induced by the irradiation. Three genotypes of groundnut; SAMNUT 21 SAMNUT 23 and SAMNUT 24 obtained from the Institute for Agricultural research were irradiated with five doses of thermal neutron irradiation, 0 Gy, 3 Gy, 6 Gy, 9 Gy and 12 Gy at the Centre for Energy Research and Training, Ahmadu Bello University, Zaria in 2013. The irradiated seeds and their respective controls were sown in a randomized complete block design with three replications in the screen house to produce M1 plants. A total of 96 M1 families generated from M1 plus three controls were evaluated using 11 x 12 augmented designs in 2014. Data were collected on plant height, number of branches per plant, days to 50% flowering, canopy spread, number of pods per plant, 100 seed weight, pod yield per plant, shelling percentage, kernel yield per plant and pod yield at M2. Significant differences (P<0.05) were observed among the genotypes for seedling traits measured in the M1 generation. Progressive decrease in seedling height and other seedling growth parameters with increase in radiation doses was observed in all the genotypes indicating their sensitivity to irradiation. SAMNUT 21 and SAMNUT 23 were found to be more sensitive to thermal neutron irradiation than SAMNUT 24 as they recorded lower survival at 12 Gy. Seedling height varied from 8.57 to 10.03 cm in materials derived from SAMNUT 21. It varied from 9.90 to 11.17 cm in SAMNUT 23 and from 10.83 to 12.50 cm in SAMNUT 24. Among the various doses, neutron irradiation at 3 Gy resulted in increases in plant height, number of pods per plant, pod yield and kernel yield per plant especially for SAMNUT 24 at M2 vi generation. The mutagenic effectiveness of irradiation doses at M2 ranged between 0.1% for 12 Gy and 2.6 % for 3 Gy. Thermal neutron irradiation at 6 Gy had higher efficiency in SAMNUT 21 (1.05 %) and SAMNUT 23 (0.72 %) while 3 Gy had higher efficiency in SAMNUT 24 (0.46 %). There were highly significant differences (P<0.01) among the plant progenies for all the traits measured at M2. In mutants derived from SAMNUT 21, pod yield ranged between 321.43 for S21-12-1 and 1537.74 kg ha-1 for S21-3-3 compared to 1081.88 kg ha-1of the control. It ranged between 1310.06 for S23-9-3 and 2649 kg ha-1 for S23-6-8 in SAMNUT 23 and varied from 876.99 for S24-12-1 to 2671.47 kg ha-1 for S24-3-10 in SAMNUT 24 compared to 1697.48 kg ha-1 and 1204.68 kg ha-1 of the controls respectively. The mutants had significantly higher variability than the controls, indicating that genetic variability was induced for the agronomic traits. The induced variability for agronomic traits measured offers possibility for future selection and improvement of these traits.