The objective of this study was to establish a breeding season and to evaluate the reproductive performance of a horse herd of the Pantaneira breed from Nhumirim Ranch in the lowlands of Mato Grosso do Sul, Brazil. During the period 1990/91, the stallion was kept year-round with 17 mares. In the following year (91/92) a breeding season of seven months (Sept. 91 to Mar. 92) was established, in which the stallion and 15 mares were used. In the first period (90/91), the concentration of births occurred from September to December of 1991. The percentage of pregnancy and parturition observed in 90/91 and 91/92 for the male:female proportions of 1:17 and 1:15 were: 82.3, 100 and 86.7, 100%, respectively. In the breeding season from Oct. 91 to Feb. 92 with male/female ratios of A-1:11, B-1:10 and C-1:10, it was observed that the percentage of pregnancy was 90.9, 100 and 100%, respectively, with 100% parturition in the 3 groups. Independently of the number of females used (A-1:10, B-1:08, C-1:12), the rate of pregnancy obtained from the breeding season from Oct. 92 to Feb. 93 was 100%.