Objectives: The aim of this study was to examine the relationship between the leadership style and collective efficacy on the effectiveness of health promotion work teams in Taiwanese elementary schools. Methods: The study design was cross-sectional. According to the size of the districts and individual schools, a stratified random sample was used to select subjects from 518 health promotion work teams approved by the Ministry of Education in 2007. Four hundred and ninety-seven subjects were recruited and the response rate was 86.32% (n=429). Structured questionnaires including demographics, leadership style, collective efficacy and group effectiveness were used to collect data. The data were analyzed using descriptive statistics, regression and SEM. p＜.05 was considered as statistically significant. Results: The leadership style had. 49 direct effect and. 32 indirect effect on Group Effectiveness through collective efficacy. The total effect of leadership style on Group Effectiveness was .81. Leadership style and collective efficacy were the major predictors as they accounted for 53.9% of the total variance for Group Effectiveness. Conclusions: Better leadership style will have direct and indirect effects on group effectiveness.