The widespread use of Internet and computer-based applications for promoting, evaluating, and researching physical activity has increased exponentially (Sciamanna et al.,2002), largely due to benefits of low cost access to large samples, administration convenience, and automated data-checking. Little has been done however, to examine the psychometric characteristics of web-based questionnaires (Lefever et al., 2007). The purpose of this study was to examine the internal consistency reliability, and construct validity of a set of Internet-administered measures commonly used in theoretically-based physical activity research. This is important, as conclusions made from Internet-based research rely on the quality of measures used. Thirty-nine women (Mage = 30.0, SD = 4.4) completed measures associated with exercise motivation (BREQ2, Markland & Tobin, 1999), physical competence (PCOMP, Fox, 1990), global self-worth (GSW, Messer & Harter, 1986), exercise locus of causality (ELOC, Markland & Hardy, 1997), body satisfaction (BSAT, Franzoi & Shields, 1984), and exercise behavior (LTEQ, Godin & Shepard, 1985), through a secure Internet web-site, prior to participating in a community-based exercise program. Cronbach alpha coefficients were calculated and compared to those reported for paper-and-pencil administrations in similar samples. Correlations were examined to provide some evidence of construct validity. Alpha coefficients calculated for the four subscales of the BREQ2 ranged from a = .73 to .93, comparable to ranges reported by Markland and Tobin (a = .73 to .86; 1994). Correlations among the Internet-administered subscales formed a perfect simplex pattern, supporting the self-determination theory motivational continuum, and use of the relative autonomy index, frequently computed to represent individuals' levels of self-determined exercise motivation in a single score (Deci & Ryan, 1985). Internal consistencies were acceptable for PCOMP (a = .89), GSW (a = .84), and BSAT (a = .84), and comparable to values reported in a similar sample (a = .87, .87, .84, respectively; Levy & Ebbeck, 2005). Internal consistency for ELOC (a = .84) was also acceptable and comparable to paper-and-pencil administration (a = .87; Markland, 1999). Correlations between PCOMP, BSAT, ELOC, and LTEQ (range, r = .30 to .65) were moderately positive. Results support the internal consistency reliability of these Internet-administered measures and provide partial evidence, for some of the measures, of construct validity. These findings provide researchers with some level of confidence in the conclusions made from Internet-based physical activity related measurement, and support their use as a viable means of quality data collection in the physical domain.Keyword(s): exercise/fitness/physical activity, measurement/evaluation, research