This study was carried out to investigate the Online Information Seeking Behaviour of Postgraduate Students (PG) in Ahmadu Bello University, Zaria. Five research questions were raised and five (5) hypothesis were formulated and tested at =0.05. The research questions sought to find out the types of online information resources and services available for use by postgraduate students, their sources of online information, their information search pattern, how they evaluate and filter the quality of online information resources (OIRs) they use. The research adopted survey method; the instrument used for data collection was the questionnaire. Null hypotheses 1, 3, 4 and 5 were analysed using ANOVA while Null hypothesis 2 was analysed using t-test. The study discovered that majority of the postgraduate students are aware of the online information resources which they frequently use. A majority of the postgraduate students are extraverted and enthusiastic by the results and amount of information they get online. This behavior affects their ability to get the required information. It is recommended that University Libraries should intensify the existing training programme for PG Students.