Background: This study reports development of a social support scale appropriate to the Vietnamese culture and the impact of social support on mothers of children with cognitive delays by using the developing scale. Method: Interview surveys were conducted with 225 mothers of children with and without cognitive delays in Vietnam. The structural and functional social supports were examined in relation to two aspects of stress, parental competence and role restriction. Demographic variables were incorporated in examining the relationships between social support and stress. Results: The social support scale had adequate reliability and structural and functional aspects comparable to those found in Western societies. Two domains in functional support, material and family-directed support, alleviated stress when controlling for child disability status and sociodemographic variables. Conclusions: The results showed that informal and functional social support have some effect on maternal stress. However, when other variables were examined in combination, child disability was the strongest predictor of maternal stress.