The purpose of this study was to determine the types of phytoplankton in Perintis Lake, Suwawa District, Bone Bolango Regency, Gorontalo Province. This research is descriptive qualitative using survey method with phytoplankton as research subject. The data collection technique was carried out by purposive sampling which was carried out 3 times with the aim of collecting data effectively. The research procedure includes observation, measurement of water physico-chemical parameters, phytoplankton water sampling, and identification in the laboratory. Data analysis was carried out descriptively by identifying the types of phytoplankton using a binocular microscope and matched to the identification book. The results of the research obtained found phytoplankton 8 divisions with 24 species (Synura sp., Pandorina morum, Ankistrodesmus densus, Tetraedron triangulare, Selenastrum bibraianum, Scenedesmus sp., Tetrabaena socialis, Dictysphaerium ehrenbergianum, Raphidiopsis raciborskii, Snowella lacustris, Merismopedia sp...), Aphanocapsa sp., Pinnularia sp., Cyclotella polymorpha, Synedra sp., Pseudostaurastrum lobulatum, Isthmochloron lobulatum, Goniochloris sp., Penium polymorphum, Staurastum gracile, Aulacoseira granulata, Cochlodinium polykrikoides, Ostreopsis sp., and Prorocentrum minimum).