A. Olivares, M. Johnston, and C. Calderon. 2009. Effect of rainfall regimes on seed production and quality of Avena barbata. Cien. Inv. Agr. 36(1): 69-76. The effects of rainfall amount and distribution on seed yield and quality in Avena barbata were evaluated in a greenhouse under controlled conditions with simulated rainfall regimes. A randomized complete-block design was used with five replications of one pot each. Seven treatments were established according to rainfall regimes for a real year in the semiarid zone in the Metropolitan Region, Chile: normal rainfall (1982), late rainfall (1987), normal-early rainfall (1962), normal-late rainfall (1989), dry-early rainfall (1981) and dry-late rainfall (1990). One treatment without water stress was left for comparison. One-year-old seeds were planted in pots with disinfected soil. The five most uniform plants in terms of size and health were chosen for the experiments. The simulated rainfalls were applied according to calendar dates of each selected year. The roots' and shoots' mass production was evaluated. The number of floral shoots, fruits and seeds; their total weights and separating annexes; as well as the number of filled seeds, seed viability and germination were also determined. Based on the results obtained, a rainy year with late rainfall distribution highly favored mass productions in addition, the seeds' quality was better in years with late rainfall distribution, normal or rainy. The proportion of filled seeds was greater in the rainy-normal rainfall year, and the seed annexes were better in the late rainy year. The results indicate that the production, quality of grains and phenology of A. barbata were modified with the rainfall distribution.