Parental stress occurs when parenting demands exceed the resources available to cope with parenting. Previous research has identified household wealth, educational level, marital status, age, and number of dependent children as predictors of parental stress. However, limited evidence exists from sub-Saharan Africa. This study investigated the sociodemographic predictors of parenting stress among mothers in Kenya and Zambia. This cross-sectional study utilised baseline secondary data from parenting intervention programs implemented in Kisumu County (rural Kenya), Nairobi County (Urban Kenya), and Chisamba District (rural Zambia). Out of 913 caregivers recruited for the parenting program, 844 with complete data were included in the analysis. The mean age was 1.0 (SD = 0.7) years. Parental stress was measured using the Parental Stress Score (PSS) tool and demographic questionnaires were used to collect demographic information. Mean PSS were compared across study sites, and a multiple linear regression model was used to examine associations between sociodemographic predictors (household income, educational level, marital status, maternal age, child age, and number of children aged < 5 years) and PSS, adjusting for clustering and other predictors. From the results, the mean PSS in rural Kenya was 37.6 [SD = 11.8], in urban Kenya was 48.4 [SD = 4.2], and in rural Zambia was 43.0 [SD = 9.1]. In addition, the significant association between PSS and mothers’ income and educational level was only observed in Kenyan study sites (income: Kenya rural β = -0.40, p < 0.001**; Kenya urban, β = − 0.33, p = .02*; Zambia rural, β = − 0.01, p = 0.7) education: Kenya rural, β = − 0.25, p = .005**; Kenya urban, β = − 0.14, p = 0.07; Zambia rural, β = 0.04, p = 0.3). However, marital status, mother’s age, child’s age, and the number of children below five years were not associated with PSS. The results revealed that mothers’ income and education level were negatively associated with PSS, indicating that higher socioeconomic status can buffer the effects of parental stress.Trial registration Pan African Clinical Trials Registry (https://pactr.samrc.ac.za/) database (ID Number: PACTR20180774832663 Date: 26/July/2018; (ID number: PACTR201905787868050 Date: 06/May/2019.