Ishizuchi‐kurocha is a postfermented tea produced in Saijo, Ehime, Japan. Harvested tea leaves are fermented aerobically by fungi. Subsequently, the tea leaves are fermented anaerobically by lactic acid bacteria. In the current study, fermentation‐related lactic acid bacteria were examined during the processing of Ishizuchi‐kurocha obtained from three producers over a period of 3 years. Lactobacillus plantarum subsp. plantarum was isolated as the dominant species in Ishizuchi‐kurocha. Lactobacillus brevis was also frequently isolated. In contrast, none of these species could be isolated from raw tea leaves. A component analysis of the tea extract was performed. The amount of catechins, amino acids, and γ‐amino butyric acid in tea leaves changed during anaerobic fermentation. L. plantarum was selected during aerobic fermentation and grew exponentially during anaerobic fermentation. And L. brevis is important for GABA formation. Our results suggest that a controlled growth of L. plantarum is essential for the processing of the Ishizuchi‐kurocha.