Supervisors have a unique function of ensuring professional service and best practices. However, few studies in Taiwan have explored the effectiveness of supervisory activities, and almost none have examined the importance, effectiveness, key influence, evaluation differences, and influencing factors of these activities from workers’ perspectives. In this study , the social welfare institutions responsible for the social service programs of various local governments as the survey units. 222 supervisors and 349 social workers were surveyed using a structured questionnaire. The statistical analyses, including descriptive statistics, independent-samples t-test, ANOVA, and importance-performance analysis (IPA), showed that “unit type” and “social work certificate” were the critical factors affecting supervisors, while “age” was the critical factor affecting the evaluation of social workers.“Ability enhancement” was regarded as a supervisory activity that meets expectations and “administrative function” as a critical factor in improving supervisory effectiveness. However, social work certificates were not a prerequisite for supervisory positions.