BACKGROUND: The stagnation and relatively low use of modern contraceptives are ongoing public health concerns in Bangladesh and other low- and middle-income countries. Although a cultural preference for sons may be linked to the current use of contraceptives, this linkage has not been adequately explored in the Bangladesh context. We investigated the effects of child sex composition on the current use of modern contraceptives. METHODS: We extracted and analysed data from 17,333 women who participated in the 2017/18 Bangladesh Demographic and Health Survey. The outcome variable was the current use of modern contraceptive methods. The study factor was the parity and sex composition of the living children. We used multilevel logistic regressions to determine the association between the study factor and outcome variables, adjusting for potential covariates at the individual-, household-, and community-levels. RESULTS: Women with relatively high parity had higher odds of currently using modern contraceptives. Among the individual parities, compared to women with no live sons, women with one or more live sons were more likely to report currently using modern contraceptives. However, this association is significant for women up to three children. When examining both parity and children's sex composition in a regression model, in each parity category, the likelihood of using modern contraceptives tend to rise with an increasing number of sons compared to women with just one daughter. CONCLUSION: The findings of this study suggest that while the use of modern contraceptives by women increases with the increasing number of children and son preference is prevalent in Bangladesh, women also want to have a mixed composition of son and daughter. The study findings can be used in family planning programmes to customise contraceptive promotion and counselling messages.