The study investigated Awareness and Utilisation of Institutional Digital Repository by Postgraduate Students of the Faculty of Science, Ahmadu Bello University Zaria. The study achieved the following objectives; To find out the extent of awareness of the Institutional Digital Repository, to identify the factors motivating the Utilisation of the Institutional Digital Repository, to find out the extent at which the Institutional Digital Repository is being utilised by the Postgraduate Students and to identify the challenges of Utilisation of the Institutional Digital Repository by the Postgraduate Students The study adopted a quantitative method for data gathering. Questionnaire was the only instrument used for the study, targeted 73 respondents selected through stratified proportional random sampling technique from a population of 1451 Postgraduate Students from nine (9) Departments of the Faculty of Science Ahmadu Bello University Zaria. Among the 73 copies of questionnaire administered 67 (91.9%) were returned duly completed by respondents. Similarly, 53 (79.1%) of the 67 respondents were males and 14 (20.9%) were females. Data from the survey was analysed using descriptive and inferential statistics of SPSS. Frequency distribution tables and percentages were used for the descriptive statistic while two (2) simple t-tests were used for the inferential statistic to test null hypothesis 1 and 2. The two hypotheses were tested all at 0.05 and 65 degree of freedom. The study discovered that, the Awareness of Institutional Digital Repository by Postgraduate Students of the Faculty of Science Ahmadu Bello University Zaria was very low so also the utilisation of the institutional digital repository, free access to the IDR was the major motivator of utilisation of IDR in A.B.U. Zaria by Postgraduate Students of the Faculty of Science that were opportuned to be aware of the IDR.Finally the study established that for Ahmadu Bello University Zaria and Kashim Ibrahim Library to attain the set goal, a maximum utilisation of Institutional Digital Repository by increased awareness campaign on the importance and the reason why the IDR was established should be provided to the entire university community.