Purpose: To explore the barriers and solutions of immunization programs for children among vulnerable classes in the position of service providers in Community health centers. Method: Data were collected through focus group interviews with 3 groups (17 providers), and were analyzed according to the analytic method of Morgan (1998) and Krueger (1998). Results: The following five categories were identified: difficulties in obtaining a list of children among vulnerable classes, difficulties in first contact with them, difficulties in up-to-date immunization, various difficulties according to the types of vulnerable family and suggestions of solution. These results indicated that there are many difficulties in providing expanded immunization service for children among vulnerable classes in terms of manpower, cooperation of departments in public health centers and linkages between health and welfare. Finally, the characteristics of the types of vulnerable family need to be elucidated. Conclusion: To increase immunization rates among children of vulnerable classes, policies need to be prepared at the public health organization itself and the linkages between health and welfare and need for hiring additional personnel.