Significance: Previous studies have found the relationship between social support (SS) and children's physical activity (PA) to vary depending on the method used to measure activity. In this research, objective monitoring has been unrelated to SS, whereas self-reported activity has been related. The research to date has objectively measured PA using accelerometers. It is unclear if similar results would be observed when using other objective measures of PA such as pedometers. The purpose of this study was to examine the relationship between SS and children's PA as assessed using self-report and objective (pedometers) measures. Methods: Forty three children (25 girls) age 10 to 11 years wore sealed pedometers for four consecutive weekdays and responded to a questionnaire assessing: past 7 day vigorous (VPA) and moderate PA (MPA) (YRBS); 3 day sweat recall (3d Sweat) (Janz et al., 1995); and SS from mothers and fathers (i.e., encouragement, done activity with, praise, transportation, watch), and peers (i.e., you encourage, peers encourage, done PA with, tease, praise) (Prochaska et al., 2002). Hierarchical linear regression models, controlling for BMI and maturation (i.e., peak height velocity), were conducted for each activity measure and provider of SS for boys and girls, separately. Results: Pedometer steps were unrelated to SS from any provider for girls, whereas dads' praise and watching explained 40% of the variance in pedometer steps for boys. Moms' praise, done activity with, and transportation to places to be active accounted for 54% of the variance in girls VPA. Moms' encouragement explained 26% in boys' VPA. Dads' praise (18%) and peers' encouragement (19%) were related to girls' VPA. Only child encouraging their peers to be active (40%) was related to boys' VPA. No support type from any provider was related to the MPA measures. Both moms' (29%) and dads' (24%) transportation, and peer praise (16%) explained a significant portion of girls past 3d Sweat. No associations were observed with boys 3d Sweat measure. Conclusions: Our results indicate the method selected to assess PA fundamentally changes the observed relationship with SS. Although objective measures are preferred when assessing children's PA (Welk et al., 2000), researchers must be aware their use is likely to result in different relationships than with self-report, subsequently altering the importance of SS. The outcome of interest – total daily ambulatory movement with pedometers or specific intensities with VPA and 3d Sweat – should therefore guide the selection of an activity measure, with both objective and self-report used when feasible. Keyword(s): measurement/evaluation, physical activity