The aim of this study was to evaluate the relative competitive ability of barnyardgrass (BYG, Echinochloa crus-galli (L.) P. Beauv.) compared to rice barnyardgrass (ECPH, E. oryzicola (Vasinger) Vasinger) against rice (Oryza sativa L.) cv. Hashemi in a replacement series study. Experiment was arranged in randomized complete block design with three replicates using a factorial treatment arrangement. Factors were two species of Echinochloa genus (BYG and ECPH) and five rice:BYG or rice:ECPH mixture proportions (8:0, 6:2, 4:4, 2:6, and 0:8). Relative yield total of aboveground dry weight, root dry weight and leaf area indicated that BYG or ECPH were competing for the same resources with ’Hashemi’. In general, replacement series curves and relative crowding coefficient (RCC) values demonstrated that both BYG and ECPH were more competitive than ’Hashemi’. BYG had significantly higher aboveground dry weight, root dry weight, tiller number, leaf area, and plant height than ECPH, when grown with ’Hashemi’. This experiment confirmed that BYG was more competitive than ECPH against ’Hashemi’.