The genomic locations and identities of the genes that regulate voluntary physical activity is presently unknown. The purpose of this study was to search for quantitative trait loci (QTL) that were linked with daily mouse running wheel distance, duration, and speed of exercise. F₂ animals (n=310) derived from high active C57L/J and low active C3H/HeJ inbred strains were phenotyped for 21 days. After phenotyping, genotyping using a fully informative SNP panel with an average intermarker interval of 13.7cM was used. On all three activity indices, sex and strain were significant factors, with the F₂ animals similar to the high active C57L/J mice in both daily exercise distance and duration of exercise. In the F₂ cohort, female mice ran significantly farther, longer, and faster than male mice. QTL analysis revealed no sex-specific QTL, but at the 5% experimentwise significance level, did identify one QTL for duration, one QTL for distance, and two QTL for speed. The QTL for duration (DUR13.1) and distance (DIST13.1) colocalized with the QTL for speed (SPD13.1). Each of these QTL accounted for approximately 6% of the phenotypic variance whereas SPD9.1, (Chr. 9, 7 cM), accounted for 11.3% of the phenotypic variation. DUR13.1, DIST13.1, SPD13.1, SPD9.1 were subsequently replicated using haplotype association mapping. The results of this study suggest a genetical basis of voluntary activity in mice and provide a foundation for future candidate gene studies.