The purpose of this study was to determine the effect of periodic walking during hindlimb suspension on the mass, relative weight, fiber type distribution and cross-sectional area of Type I and II fibers in the developing Type II plantaris muscle. To examine the effectiveness of periodic walking on mass and fiber size, the hindlimbs of young female Wistar rats were suspended(HS group) and half of these rats walked on a treadmill for 45 min/day(15 min every 4 hours) at 5 meters/min at a 15 degree grade(HS-W group) After seven days of hindlimb suspension, the plantaris muscle wet weight was 28.40% significantly smaller (P<0.005) and relative plantaris muscle weight was 26.97% smaller compared with those of control rats(P<0.05). The plantaris muscle wet weight and the relative plantaris muscle weight increased by 46.60% and 49.23% respectively with periodic walking, moreover, the plantaris muscle wet weight and the relative plantaris muscle weight of the HS-W rats recovered to the level of the control rats. No change was observed in fiber type percentage of the developing plantaris muscle following one week of hindlimb suspension or periodic walking during hindlimb suspension. Type I and II fiber cross-sectional areas of the developing plantaris muscle were 42.51% and 43. 68% lower in the HS group than in the control group(p<0.0001), Type I and II fiber cross-sectional areas of the developing plantaris were 30.82% and 45.97% greater in the HS ?W group than in the HS group(p<0.0001), whereas Type I and II fiber cross-sectional area of HS-W group were less than those of the control group(P<0.0001) The results suggest that periodic walking can attenuate developing plantaris muscle atrophy induced by hindlimb suspension.