Seed production is the limiting factor for hybrid rice expansion. The hybrid parents' outcrossing ability is the key point to increase seed production. To breed for outcrossing ability, it is necessary to dispose of variability and evaluate, as soon as possible (S 1, S2), this character. Estimation of female outcrossing ability is possible for lines segregating for a recessive male-sterile gene. The grain yield of male-sterile plants, outcrossed by fertile plants, either of the same line or by fertile plants of another line, is an estimation of outcrossing ability. Using this first method, we evaluated the outcrossing ability of 62 S2 lines coming from a cross between two inbred lines (one msms). With the second method, we evaluated outcrossing ability of 130 S1 lines extracted from a recurrent population segregating ms gene. The 130 lines were outcrossed by four testers: three inbred lines and a population. Significant differences were observed among S2lines (outcrossing ability ranged from 2% to 54%). A good correlation was observed between outcrossing by each tester. For both trials, an important variability was observed. Selection for female outcrossing aptitude is thus possible and important genetic progresses are to be hoped. Outcrossing ability evaluation of future B lines, at S1 and S2 stages, is now integrated into all breeding programs that CIRAD and its partners lead in Latin America. This outcrossing ability evaluation method can be used for phenotyping lines, allowing molecular breeding to speed up creation strong of A and B lines with strong outcrossing ability.