This study presents a method that combines both dimensional analysis and statistical regression analysis for predicting the shear capacity of slender reinforced concrete (RC) beams without web reinforcement taking the size effect into consideration. This method incorporates the modified Buckingham-PI theorem (Butterfield, 1999, Geotechnique 49(3), 357-366) to formulate two mathematical models for predicting the shear capacity at the formation of diagonal tension cracks and at the ultimate shear strength. The results of the two models are compared with several sets of existing experimental results. This study shows that the variations in the experimental results of shear capacity of slender RC beams ( a / d  2.5 ) defined at the formation of diagonal tension cracks of beams can be explained by the variations of the concrete tensile strength and the variations in the experimental results of ultimate shear strength of slender RC beams ( a / d  2.5 ) can be explained by the variations of the concrete splitting strength
