Examination of overweight by race indicates Mexican American boys are the most overweight and Mexican American girls the second most overweight ethnic groups of U. S. children, with estimates of 23% of boys and 27% of girls overweight (Strauss & Pollock, 2001). A well-established benefit of physical activity among children is its ability to aid in weight control and fat reduction; however, Mexican American boys and girls have higher physical inactivity rates than their Black or non-Hispanic white counterparts (Anderson et al., 1998). As a theoretical construct, locus of control is one's generalized expectancy to perceive reinforcements as being either dependent upon one's own behavior (internal control) or contingent upon forces beyond one's control (external control). The purpose of this study was to extend the literature dealing with participation determinants through examining the association of locus of control, current exercise level, age, gender, and body mass index (BMI) with intention to be physically active among Mexican American children. The sample consisted of 216 boys and 185 girls ranging in age from 10 to 15 years. Subjects were drawn from an educational program held on the University of Texas-Pan American campus. Data were collected through a self-report survey instrument and height and weight measures to calculate BMI. Exercise-specific locus of control (internal and external powerful others) was assessed using an adapted version of the Exercise Locus of Control scale (McCready & Long, 1985); exercise level was measured by a statement asking how may times a week the respondent played or exercised enough to make him/her sweat or breathe hard (CDC, 1997); and activity intention was determined by a statement asking the respondents' degree of agreement/disagreement with planning to engage in vigorous exercise during the next 4 weeks (Ajzen & Fishbein, 1980). Structural equation modeling was used to test for variable associations. Analysis indicated that among boys, intent was associated with exercise level (beta=.35, p<.01), exercise level with BMI (beta=.24, p<.01), BMI with age (beta=.18, p<.05), and age with powerful others (beta=.15, p<.05). Among girls, intent was associated with exercise (beta=.17, p<.05), BMI with age (beta=.21, p<.o1), and age with powerful others (beta=.26, p<.01). Results suggest that for both Mexican American boys and girls, current exercise involvement has the greatest influence on intent to be physically active and age has a mediating effect due to the increased importance of the powerful others exercise control belief as one becomes older. Keyword(s): exercise/fitness, multiculturalism/cultural diversity, physical activity