Abstract: Context/Background: Given the current socio-economic conditions of the Nigerian nation-state, it is logical to say that the resources needed to cater for its ever-growing population are limited and the trend has moved the nation to adopt an anti-natalist policy. However, there is a paucity of empirical studies on the influence of family structure, as an intergenerational factor, on fertility behavior in South- Western Nigeria and thus, this study investigates the association between family structure and fertility behaviour in Lagos. Data Sources and Methods: A cross-sectional survey was conducted among 185 married undergraduates of the Distance Learning Institute at the University of Lagos, Lagos State, Nigeria. Multi- stage and simple random sampling was employed in selecting the respondents. Findings: The study revealed that the size of an individual’s family of orientation (O.R. = |.22) and income (O.R. = 1.40) are predictors of the individual’s fertility and fertility preference. Conclusion: Attention should be given to the socio-economic factors that shape fertility behaviour and the immediate and unmet need for contraception among couples. Keywords: Fertility behaviour, Fertility, Fertility preference, Family structure