BackgroundPostnatal depression (PND) is a universal mental health problem that prevents mothers' optimal existence and mothering. Although research has shown high PND prevalence rates in Africa, including Kenya, little research has been conducted to determine the contributing factors, especially in low-resource communities.ObjectiveThis study aimed to investigate the PND risk factors among mothers attending Maternal and Child Health Clinics (MCH) in the slums, Nairobi.MethodsThis study is cross-sectional, which is a part of a larger study. A sample of 567 mothers of 6-10 weeks postnatal from two Maternal and Child Health (MCH) formed the study population. The Depression rate was measured using the original 1961 Beck's Depression Inventory (BDI). In addition, a sociodemographic questionnaire (SDQ) was used to collect hypothesized risk variables. Results The PND prevalence rate was 27.1%. Women with: unplanned pregnancy (AOR=1.87, 95% CI 1.02, 3.43), unemployed (AOR=4.43, 95% CI 1.01, 19.76), dissatisfied with body image (AOR=2.51, 95% CI 1.21, 5.19) and feeling fatigued (AOR=2.02, 95% CI 1.06, 3.85) had higher odds of developing PND. ConclusionThis study builds upon scarce previous studies on PND from low-income countries. Identifying specific PND risk factors may help in devising targeted prophylactic and therapeutic strategies.