Mothers living in slums are vulnerable to malnutrition and poor dietary diversity. Dietary diversity plays a crucial role in the fulfillment of both micro and macronutrient requirements. This cross-sectional study aimed to assess the status of and factors associated with dietary diversity. The study included 332 mothers from four slums in Dhaka city. Trained enumerators collected data from 19 November till 1 December 2016. Dietary diversity (DD) was measured by asking questions about the consumption of 10 food groups in the last 24 hours. The mean age of mothers was 23.3 (±4.7) years. The mean number of food groups consumed by mothers in the previous 24 hours was 4.54 (±1.79) out of 10. The prevalence of poor DD (<5 food groups) was 55.1%. In the multivariable model, staying in the slum for 25-60 months [AOR= 2.3, (95% CI: 1.16, 4.67)], being in the poorest [AOR= 4.8, (95% CI: 1.84, 12.38)] and poorer [AOR= 3.8, (95% CI: 1.41, 10.09)] socio-economic status (SES) quintile and having average nutrition knowledge [AOR= 1.9, (95% CI: 1.01, 3.47)] were significantly associated with mother’s poor DD. The predictive model showed differences in the probability of poor DD across SES (poorest=47% and richest=16%) reduced when good nutrition knowledge was introduced in the model. SES and nutrition knowledge is therefore associated with dietary diversity among these mothers with young children. Platforms such as electronic media and slum-based groups could be used to promote nutrition education whereas food subsidies especially for fruits and vegetables could help to enhance dietary diversity among mothers.