To meet the 2030 goal to end all types of malnutrition, thoroughly investigating and addressing context-specific factors of undernutrition is crucial. Therefore, this study assessed the prevalence of undernutrition and associated factors among children aged 6β23 months in South-East Ethiopia. A community-based cross-sectional study was conducted on 580 randomly sampled motherβchild pairs in February 2022. Socio-demographic, dietary intake, household food security (HFS), maternal knowledge and practices of child feeding, and the child's weight and height data were collected. A multivariable logistic regression analysis was done. The prevalence of stunted, wasted, and underweight children was 32β
1, 7, and 9 %, respectively. Being male (AOR = 1β
75), not using the growth monitoring and promotion (GMP) service (AOR = 1β
50), household food insecurity (HFI) (AOR = 1β
67), lack of improved water (AOR = 2β
26), and bottle-feeding (AOR = 1β
54) were significantly associated with stunting. Being male (AOR = 3β
02), having low maternal knowledge on child-feeding practices (AOR = 3β
89), not listening to the radio/television (AOR = 3β
69), having a history of fever (AOR = 3β
39), bottle-feeding (AOR = 3β
58), and HFI (AOR = 3β
77) were significantly predicted wasting. Being male (AOR = 3β
44), not using GMP service (AOR = 2β
00), having a history of fever (AOR = 4β
24), lack of knowledge on optimal breastfeeding duration (AOR = 3β
58), low maternal knowledge on child feeding (AOR = 2β
21), HFI (AOR = 2β
04), and lack of improved water (AOR = 3β
00) showed significant association with underweight. In conclusion, stunting is alarmingly common while wasting and underweight are sub-optimal. Prevention of infectious disease, providing basic education for fathers, ensuring HFS; enhancing media access, maternal knowledge about IYCFP and improving water access; and GMP service utilisation are crucial to improve child nutrition.