Introductionsub-optimal birth spacing is higher in sub-Saharan countries including Ethiopia. It can affect the economic, political and social aspects of a given country. Therefore, this study aimed to assess magnitude of sub-optimal child spacing practice and associated factors among childbearing women in Southern Ethiopia.Methodsa community based cross-sectional study was conducted from July to September 2020. A random sampling technique applied to select kebeles, and systematic sampling was employed to recruit study participants. Data were collected by pretested and interviewer administered questionnaire through face-to-face interviews. Data cleaned and checked for completeness, and analyzed by SPSS version 23. A p-value of < 0.05 was considered as cutoff point to declare the strength of statistical association with 95% of CI.Resultsmagnitude of sub-optimal child spacing practice was 61.7% (CI: 57.7: 66.2). Not attending formal education (AOR= 2.1 (95% CI: 1.3, 3.3), family planning utilization for less than 3 years (AOR= 4.0 (95% CI: 2.4,6.5), being poor (AOR= 2.0 (95% CI: 1.1, 4.0), breastfeeding of less than 24 months (AOR= 3.4 (95% CI: 1.6,6.0); having more than 6 children (AOR= 3.1 (95% CI: 1.4,6.7); and waiting time ≥30 minutes (AOR= 1.8 (95% CI: 1.2,5.9) were predictors of sub-optimal birth spacing practices.Conclusionsub-optimal child spacing was relatively high among the women of Wolaita Sodo Zuria District. Improving utilization of family planning, expanding all inclusive adult education, delivering community based continuous education on optimum breast-feeding practice, involving women in income generating activities, and facilitated maternal services were recommended to fill the identified gap.