Background: Childhood malnutrition as a major public health problem among children in developing countries can affect physical and intellectual growth and is also considered as a main cause of child morbidity and mortality. The objective of this study was to estimate the prevalence of under-nutrition and identify determinants of malnutrition among children under 6 years of age in Fars province, Iran. Methods: This survey was conducted by house to house visit through multi-stage sampling in 30 cities of Fars province, during December 2012 to January 2013. A total of 15408 children, aged 0-6 years old, were studied for nutritional assessment in terms of underweight, stunting, and wasting. Also, socio-demographic measures were obtained from structured questionnaire. Backward stepwise logistic regression was used to relate underlying factors to the odds of under-nutrition indices. Results: The rates of stunting, underweight, and wasting were 9.53, 9.66, and 8.19%, respectively. Male children were more stunted compared to females (OR= 1.41, CI: 1.26-1.58). Also, stunting was significantly associated with lower family income (OR= 3.21, CI: 1.17-8.85) and lower maternal education (OR= 0.80, CI: 0.64-0.98). Living in urban areas, and poor water supply were identified as significant risk factors of all three types of childhood under-nutrition. Moreover, Khamse and Arab ethnic groups were more vulnerable to under-nutrition. There was a suggestion that non-access to health services were associated with wasting (OR= 1.87, CI: 1.39-2.52) and also large family size was related to underweight (OR= 1.35, CI: 1.10-1.65). Conclusion: The prevalence of under-nutrition in the study population was categorized in low levels. However, planning the public preventive strategies can help to control childhood under-nutrition according to underlying factors of malnutrition in the study population including gender, settlement area, family size, ethnicity, family income, maternal education, health services, and also safe water supply
