This research was performed at the Seed Analysis Laboratory of IPAGRO/RS and at the Plant Pathology Lab of UFRGS, in Porto Alegre, Brazil. The tests were performed with six samples of rice grains CVS. CB-IRGA 409 and BR.IRGA 410. The samples, with 1kg each, were homogeneized and reduced to working samples of 100g and submitted to purity tests. The components of purity were observed for the presence of fungi after incubation for seven days at 22-30oC temperature range and a day lenght of 12 hours. The method used was the blotter test. The components observed on the purity analysis were: pure seeds, other seeds, and inert materiais. The higler population of microrganisms was defected on the samples of the cultivar BR.IRGA 409. The most frequent fungi observed were: Curvularia spp., Phoma spp., Rhynchosporium oryzae, Tilletia barclayana and Trichoconis padwickii. The ocourrence of fungi decreased in the following order: Aeschynomene rudis, red rice, Echinochloa sp., black rice and inert material.