Background <p>Single-parent households, particularly those headed by mothers, have become increasingly common worldwide due to shifts in marriage and partnership patterns. In Zambia, the rate of single motherhood has increased, exposing children in these households to unique challenges, such as economic hardship and limited access to resources, which heighten their risk of undernutrition. Despite the significance of this issue, research on the association between single motherhood and child nutritional status in Zambia remains limited. This study examines the association between single motherhood and child undernutrition in Zambia, providing policy-relevant insights.</p> Methods <p>This cross-sectional study analyzed data from three rounds of the Zambia Demographic and Health Survey: 2007, 2013-14, and 2018. The final analytical sample included 25,093 children under five years of age, born to 17,740 mothers, with information on family structure and nutritional status. Single motherhood was defined as mothers who were never married, or were divorced, widowed, or separated, while married or cohabiting mothers served as the reference group. We employed a multivariate multilevel logistic regression model to estimate the association between single motherhood and child undernutrition, adjusting for a range of demographic and socioeconomic factors.</p> Results <p>Children of single mothers had significantly higher odds of stunting (AOR = 1.146, <i>p</i> = 0.004) and wasting (AOR = 1.216, <i>p</i> = 0.034) than those in dual-parent households. Boys in single-mother households were particularly vulnerable, with increased risks of stunting (AOR = 1.186, <i>p</i> = 0.011), underweight (AOR = 1.196, <i>p</i> = 0.018), and wasting (AOR = 1.362, <i>p</i> = 0.019), while these associations were not statistically significant for girls. Among different categories of single motherhood, children of widowed mothers faced the highest risk of stunting (AOR = 1.400, <i>p</i> = 0.012) and underweight (AOR = 1.408, <i>p</i> = 0.022).</p> Conclusions <p>Single motherhood, particularly widowhood, is associated with a higher risk of undernutrition among children under five in Zambia, with boys being disproportionately affected. These findings underscore the need for targeted policies and interventions to address the specific vulnerabilities of single-mother households and reduce socioeconomic disparities to mitigate nutritional risks for children.</p>