Red rice forms are the worst field weeds in all ricecultivation areas. Early diagnosis of red rice in the primary rice seeds is a task of paramount importance a solution of which directly affects the quality of produced rice culture seeds. Red and reddishbrown colors of the caryopsis pericarp are determined by at least two loci: Rc and Rd, if the latter is expressed in conjunction with the Rc gene. In this paper, the intragenic codominant molecular marker for the Rc gene was developed and tested on the rice cultivars contrasted by the trait studied. Its effectiveness was shown in the screening of 1142 rice families of 120 plants in each.