Background: Fat mass is variably associated with bone mass, possibly due to differential mechanical and biological effects of fat mass. We examined the association of fat mass with bone mass in a lean population. Objective: To investigate association between hip bone mineral density and fat and lean mass in a cross-sectional study from southern India. Design: The Andhra Pradesh Children and Parents Study is a prospective cohort study in Hyderabad, India. In 2009-2012, the study collected data on anthropometric measures, bone mineral density (BMD), fat mass, and lean mass measured by dual-energy x-ray absorptiometry, and socioeconomic data of the adult participants (n = 1760; mean age = 34.9 years old for women; 2130 and 32.3 for men). Results: The median BMI (kg/m2) was 20.1 kg/m2. Women had relatively higher fat mass as compared to men. In models adjusted for lean mass, there was an association between hip bone mineral density and fat mass in women (β (95% confidence interval): premenopausal 0.025 (0.006 to 0.045); postmenopausal 0.045 (0.014 to 0.076)) but not in men (0.001 (-0.012 to 0.0014)). The association between hip BMD and fat mass was stronger in postmenopausal than premenopausal women. Hip BMD was consistently associated with lean mass, in both men and women. Conclusions: In this relatively lean population, lean mass was more consistently associated with hip BMD than fat mass. Weight gain through lean mass improvement may be a more reliable public health strategy for strengthening bone health in transitional settings.