Silicon carbid is considered as one of the stiffest materials for reinforcement in composites. Silicon carbid nanowiskers that recently manufactured in ceramic family industries, is going to be highly considered in ceramic matrix composites because of its high L/D ratio. But this material doesn’t commonly use in polymer matrix composites yet. So in present research, nanowiskers use as reinforcement to strenghing polypropylene fiber. then mechanical, reometrical and thermal properties of these fibers have been measured and results compaired with fibers containing sic nanoparticles Each kind of nanoparticle and nanowisker has been mixed by means of twin screw extruder in 0.2, 0.5, 0.8 and 1.1 weight percent to reach a good dispersion in polymer. Also with the tanguchi method for decrease the number of experience, just samples contains 0.2 and 0.8 percent nanoparticle and samples contains 0.5 and 1.1 percent nanowisker be under surface modification. Finally effect of sic nanoparticles or nanowiskers addition on the physical and mechanical properties of polypropylene fibers has bee studied with tensile, SEM, DSC and FTIR tests. Results shows that for undrown fiber contain nanowiskers, elongation at break lower than fibers composed with nanoparticles; because nanowiskers could not orient along the fiber axis. Here a wonderful observation is that SEM images of vertical cut off undrown fibers containing nanowiskers shows a core-skin phenomenon. Also it clearly observe that increase in nanoparticle percentage up to 0.5 weight percent, improve mechanical properties and after that because of arising nanoparticle agglomeration, it start to decrease. In fibers contain nanowiskers maximum strength is 22.7 percent with 0.2 percent reinforcement. But for fibers that have been drown up to fifth as much as original length, results is completely different; so that mechanical properties of these drown fibers contain nanowisker become greater than fibers contain nanoparticle, because nanowiskers oriented along the longitudinal direction of fiber as the reason of tension. The greatest amount of improvement in modulus test for fibers contain 0.8 percent nanowisker is 81.5 percent. Also maximum of strength test again happen in the same percent of reinforcement is 61.8 percent. The best condition calculated at modulus test in taguchi method obtain from fiber contain 0.8 percent non modified nanowisker. Also the best condition at strength test obtain from fiber contain 0.2 percent non modified nanowisker. For elongation test fibers contain 0.8 percent non modified nanowisker, give the best result. An unexpected observation in this research is that mechanical properties of samples contain modified sic is worse than fibers contain non modified sic. This happen because of increasing crystallite nucleation in modified sic makes fiber's crystals bigger. Amount of modulus variations in fibers containing nanoparticle, follow the caron model. But its variations in fibers contain nanowisker goes nearby cox model.