The purpose of this study was to understand compartively the educational professional commitment of the teachers of self-contained mentally retarded classes and regular classes in Taiwan and to investigate the relationship between teacher's background (personal, familial, school, social) variables and professional commitment. Adopting from several available resources, the "Educational Professional Commitment of Teachers in Elementary Schools Inventory" was developed in the study as an instrument. Cluster stratified random sampling was used in the investigation. Data were collected from the teachers of 196 self-contained mentally retarded classes and 292 regular classes. The obtained data were analyzed by two-way MANOVA and multiple stepwise regression. Three dimensions were illustrated in the study; including involvement, professional identity and intent to stay. The conclusions drawn from the study are as in the following: 1.The educational professional commitment of the teachers from self-contained mentally retarded classes and regular classes were found excellent, but there was a significant difference in professional identity between them. 2.The variables of most of the teacher's background in this study are the significant predictors of professional commitment. Recommendations were made to base on the findings of the study, for teacher cultivating institution, education administration, principals and school administrators.