Abstract: The need to determine the effect of family size on body weight and Packed Cell Volume (PCV) of adolescent female secondary and university students in Abia State, Nigeria, is very important for this study. One hundred and sixty adolescent girls aged 10-19 years were used for the study. Data for this report was obtained from a cross-sectional survey of two boarding secondary schools [one school from Umuahia North Local Government Area (LGA) and the other from Ikwuano LGA] and two tertiary institutions (one school from Umuahia North LGA and the other from Ikwuano LGA) in Abia State, Nigeria. A structured self-administered questionnaire designed to collect information on socio-economic status of adolescent girls was given to the respondents in their schools. A sample of 160 adolescent girls was used for body weight and iron status of the blood. Forty adolescent girls were systematically selected from each school. Pearson’s correlation was used to determine the interrelationship between variables. Results showed that the secondary school girls had larger family size than their university counterparts (41.75% vs 40.0%) respectively. The secondary school adolescents also had lower mean body weight which differed significantly from those of the university students (p<0.05). The mean PCV of both the secondary school and university students were low and comparable (p>0.05). For the secondary school students, Pearson’s correlation showed that family size had negative but significant relationship with PCV (r = -0.362, p<0.05). Body weight had negative but significant relationship with PCV (r = -0.164, p<0.05). For the university students, family size had negative but significant association with body weight and PCV (r = -0.380, p<0.05 and r = -0.008, p<0.05) respectively. This study showed that family size had an effect on body weight and PCV of both secondary school and University adolescent girls in Abia State.