A protozoan with the algophagous capability was isolated from the water samples of Dianchi Lake. Based on the morphological and genetic characteristics, it was identified as Ochromonas sp. The main factors influencing the grazing properties of Ochromonas sp. including algae species, protozoa concentration, culture temperature, time, pH and phenol concentration were investigated. The results showed that Ochromonas sp. had a strong grazing capability on Microcystis wesenbergii. When Ochromonas sp. was cocultured with M. wesenbergii for 6 days, the removal rate of M. wesenbergii was above 90%. Meanwhile, the grazing effect was enhanced with the increase of the initial concentration of the protozoa, and the best grazing capability was found when the culture pH and temperature were 4-7 and 25-35 ℃, respectively. However, high concentration of phenol could inhibit and kill the Ochromonas sp. The Ochromonas sp. was easy to culture and it reproduced rapidly. Therefore, it could be applied to control the water bloom of M. wesenbergii.