Sixteen female rats of the Fischer line were administered a series of treadmill training for eight weeks(5 times a week, 60 minutes a session a day) at a 15-degree gradient and at the velocity of 23m/min. Then their leg skeleton’s soleus muscle and plantaris muscle were extracted. Dyeing methods like myosin ATP ase. SDH and Amylase PAS were employed no a microscopic basis in order to determine the composition, transection volume, and capillary development of SO(superb activation of oxidizing enzymes), FG(excellent activiation of sugar enzymes). and FOG(mediating muscles) fibers. The analytic results are as follows. 1. Body weight increasd significantly(p<.01) in the training group compared with the control group. 2. Both m.soleus and m.plantaris increased with significance(p<0.0∼p<.01) in absolute and relative muscle weight as well 3. Even though m. soleus didn’t have anychange of fiber composition in the two group. m.plantaris was noteworthy. In its deep region. SO fibers were the same. FOG fibers increased(p<0.05) and FG fibers decreased(p<0.01). In the peripheral region, the two group had few SO fibers, while the training group’s FOG fibers grew(p<0.01) and FG fibers lowered(p<0.01). This phenomenon may be account for by FG fibers transfer to OG fibers 4. A significant(p<0.05∼p<0.01) increase of transection volume was noticed in SO) and FOG fibers of m.soleus as well as SO, FOG. and FG filers of m.plantars. The difference among the fibers was seen in the peripheral region of m.plantaris only 5. As to the barometer of muscle fiber capillary. CD and CF rato were not affected by the endurance training. Excepting FG fibers of m.soleus. CC increased(p<0.01∼p<0.001), which implies the increase in oxidizing capacity of muscular fibers. 6. Since the effect of the training in a capillary development was clearly identified by the values of muscle fiber transection volume divided into CC, any type of muscle fiber discussed here seems to have been influenced by the endurance treadmill running.