Cyanobacteria are accompanied by many bacteria in the mucus zone of the vegetative cell. A strain of Anabaena macrospora (A. macrospora) producing an earthy-musty odor was isolated from Lake Biwa together with 28 isolates of bacteria. Based on preliminary test results, 18 isolates were selected for incubation in a one-tenth Tripto-soy broth solution, and their genera and species were identified. Four isolates belonged to Alcaligenes, nine to Pseudomonas, four to Moraxella and one was not identified. Four isolates, Alcaligenes sp., Alcaligenes eutrophus, Moraxella sp. and Alcaligenes faecalis (A. faecalis) had a direct influence on the growth of A. macrospora and geosmin production. As the multiplication of bacteria was faster than A. macrospora, the consistencies of the bacteria cells and the period of bacteria addition had no influence on the final growth of A. macrospora and geosmin production.