Background: Children are essential assets of a country, because they are the future human potential required for its future development. Children belong to 5-15 years ago group are vulnerable because of their rapid growth rate. In the absence of parents, orphanages are an alternative, which provide care and support for these vulnerable children. An estimated 153 million children in the world are orphans. Being an orphan may make children more vulnerable to under nutrition as maternal and paternal level factors, and household food availability which are linked to child nutritional well – being are more likely to be inadequate. Objective: As there is a paucity of data on the nutritional status of the orphan children as a whole, especially among the Muslim population in India, we have conducted a preliminary study on the nutritional status (based on thinness) of the Muslim Orphan boys of Kolkata. Besides, it will also help to generate relevant information and data on health status of children living in orphanages. Materials and methods: This cross sectional study was conducted on 150 boys of the orphanage within the age groups of 8 to 15 years from Calcutta Muslim Orphanage, Kolkata, India. Results: Based on thinness, irrespective of grade, 32.0% boys of the studied participants were undernourished. Out of this, 2.0% orphan boys were severely undernourished (Grade III) and 9.3% were moderately undernourished whereas, 20.7% boys were in Grade I condition. Conclusion: Although, the prevalence of under nutrition as measured by low BMI for age (thinness) was not so alarming but, in comparison with other studied on orphan children from various countries, it is not in a healthy position and the result could be useful to nutrition policy makers and intervention planners to target children who are more vulnerable to under nutrition.