Ethnic community variations in over-family size affect not only ethnic family and community life but also influence national development and social welfare functions in Bangladesh. Based on optimum population theory the government of Bangladesh has adopted two-child (either male or female) family size policy. To achieve this goal mentioned in the policy family planning and contraceptive services have been providing to the eligible couples since 1971. But data collected over the 1974-2011 census periods reveal that although average over-family size is gradually shifting into smaller one, average family size of majority ethnic Muslim community over the census periods is higher than that in the other religious ethnic groups (e.g., Hindu, Christian Budhist). Using census 1974-2011 data this seminal paper describes ethnic community variations and changes in over-family size in Bangladesh. Based on the description new social policyprograms and social workers' role across the individual, group, and community level are discussed to achieve optimum family size for meeting human needs and healthy ethnic family adaptation in Bangladesh.