The relationships between fat mass (FM), lean mass (LM), and bone mass are complex with significant implications for obesity, sarcopenia, and osteoporosis later in life. While greater LM is associated with higher bone mineral density (BMD), the association between FM and BMD is less clear. Such relationships warrant further investigation especially in Asians who have higher risk of metabolic diseases and osteoporotic fractures compared to Western populations. This study investigated the associations of LM, FM and modifiable risk factors with BMD in Asian women aged 18-45 yr. 191 women from the Singapore Preconception Study of Long-Term Maternal and Child Outcomes (S-PRESTO) cohort study underwent dual-energy x-ray absorptiometry scanning at the first study visit for BMD and body composition measurements. LM, FM and four body composition phenotypes derived from dichotomizing LM and FM were related to cohort specific Z-scores of BMD at femoral neck (BMDFN), lumbar spine (BMDLS) and whole-body (BMDWB). Adjusting for covariates, LM showed positive associations with Z-BMDFN, [β (95%CI)], [0.38 (0.22, 0.55)], Z-BMDLS, [0.43 (0.25, 0.62)] and Z-BMDWB, [0.63 (0.44, 0.81)]. FM by contrast showed an inverse association only with Z-BMDWB, [−0.39 (−0.58, −0.20)]. Compared to women with healthy body composition (higher LM-lower FM), women with lower LM-higher FM had similar BMI, mean(SD) 20.9(1.5)kg/m2 but disproportionately higher percent fat, 38.4 (2.2)%, and lower Z-BMDFN, [−0.58 (−0.97, −0.18)], Z-BMDLS, [−0.41 (−0.81, 0.00)] and Z-BMDWB [−0.66 (−1.06, −0.25)]. Chinese women had lower BMD than Malay women. Physical activity and education attainment were positively, while the age of menarche was negatively associated with BMD. These findings in young women underscore the importance of early interventions recognizing ethnic differences in BMD to improve lifecourse musculoskeletal health. Most importantly, intervention strategies for Asian women should focus on healthy body composition beyond BMI, with a goal to preserve or increase LM.