Self-determination theory (SDT) (Deci & Ryan, 2000) explains human motivation by focusing on the importance of behavioral regulation based on three basic needs: the needs for competence, autonomy, and relatedness. Self determination is a process in which an individual self-regulates his/her action to satisfy one or all of the needs. This process is characterized by six components: amotivation, external regulation, introjected regulation, identified regulation, integrated regulation, and intrinsic motivation. The purpose of the study was to determine the extent to which middle school students' satisfaction of the needs for autonomy, competence, and relatedness contributed to their self-regulated motivation in physical education. Participants were 297 6th grade students from 15 middle schools randomly selected from 38 middle schools in a large metropolitan area. Data on learner need satisfaction and types of self-regulations were collected during students' regular physical education classes. The data were analyzed using a two-step structural equation modeling method. The results suggested that students' satisfaction in autonomy and competence accounted for a large portion of variability in intrinsic motivation (R2= .477) and in identified regulation (R2=.490). Satisfaction in autonomy also contributed to introjected regulation. However, satisfaction in any of the needs did not contribute to the external regulation. The model goodness-of-fit testing yielded acceptable model-data fit indexes for both the measurement model (SRMR=.066 & RMSEA=.055) and structural model (SRMR=.071 & RMSEA=.056). It was also found in the model that satisfaction in competence need was negatively associated with amotivation. This finding supports the notion that the more satisfied a student is with his/her competence, the less likely he/she will be in an amotivation state. The model also revealed an unexpected and rather surprising finding: the satisfaction in relatedness contributed to amotivation in physical education. This finding suggests that cautions need to be taken when we promote social interaction and peer relationships in physical education classes. Taken together the model allows us to identify components in the SDT that may or may not contribute to self-regulated motivation in physical education.Keyword(s): middle school issues, physical education PK-12