Experimental and analytical investigations were conducted regarding the scale effect of the tensile stress-strain relationship of steel fiber reinforced concretes (SFRC). The analytical study is based on an estimation of the relationship by means of a flexural analysis considering the tensile resistance of the SFRC. The scale effect of the relationship was considered with reducing both of the stress and strain by the ratio of the flexural strength to a small beam specimen. In order to investigate the applicability of the present method, flexural tests of reinforced concrete (RC) beams with the SFRC were performed. As the results, the reasonable agreement between the measurement and calculation of a moment-curvature relationship was obtained.