The phenotypes related to tea gray blight resistance were evaluated by the artificial inoculation method in the accessions of tea germplasm preserved at the National Institute of Vegetable and Tea Science in Makurazaki, Kagoshima Prefecture. The genotypes of 453 plants including 89 main tea cultivars in Japan were also determined by using the parent-offspring genetic analysis of many cross combinations. A wide variation in the resistance of tea plants to tea gray blight was observed both in terms of phenotypes and genotypes. The majority of the Assam plants (Camellia sinensis var. assamica) showed a high level of resistance and very few variations, both in genotypes and phenotypes. The Japanese native plants (C. sinensis var. sinensis) showed a wider genetic diversity than any other groups of plants in the resistance to tea gray blight. Since many of the tea plants derived from other countries were highly resistant to the disease and harbored 2 Pl₁ genes which confer a high level of resistance, they are very important materials for the breeding of cultivars that are resistant to the disease. The phenotype and genotype analysis was found to be very useful to identify doubtful cultivars.