In ferritic stainless steels, the amount of Cr is moderately controlled to have good corrosion resistance in applied environment. However, it also affects the yield strength of ferritic stainless steels through solid solution strengthening and grain refinement strengthening. Until now, some researches have been performed using commercial stainless steels but the obtained results contain the effect of solute interstitials (C and N). In this paper, the influence of Cr on the above both strengthening mechanism was discussed by using interstitial free ferritic stainless steel in which carbon and nitrogen are completely fixed as Ti(C,N). A previous paper has reported that the addition of chromium gives different influences to the Hall-Petch coefficient depending on the amount of Cr. However, our research has reveals the fact that the change of Hall-Petch coefficient is not due to the effect of chromium but due to small amount of carbon which exists as an impurity in ferritic stainless steels. It was concluded that chromium itself does not give any influence to the Hall-Petch coefficient of ferritic iron.