Abstract: Five microalgae commonly found in China’s freshwater ecosystems were used as experimental objects in the present study. The growth performance of individual species was examined and quantified, and the competitive ability of individual species was predicted based on its obtained growth parameters. The competition experiment was then performed, with observed competitive outcome compared with predicted results. The findings showed that based on growth parameters of these microalgae, the rank of microalgae in regard to the competitive ability follows the order of Selenastrum capricornutum > Actinastrum hantzschii > Pediastrum sp. > Scenedesmus quadricauda > Cosmarium sp. The observed competitive outcome was mostly consistent with these predictions. For example, Selenastrum capricornutum was a superior competitor, whereas Actinastrum hantzschii and Pediastrum sp. exhibited similar competitive abilities. However, Cosmarium sp. did not always perform as an inferior competitor, suggesting that the initial density of microalgae may have imposed certain impacts on the outcome of interspecific competition.