Abstract: A method of isolation of polyhydroxyalkanoates from biomass pre-cleans the biomass in a first extraction process by extracting components of the biomass other than polyhydroxyalkanoates. In a second extraction process, polyhydroxyalkanoates are extracted from a solid phase of the biomass obtained in the first extraction process by adding an extraction agent to pre-cleaned biomass based on chlorinated hydrocarbon, carrying out the extraction for 5 to 90 minutes at a temperature in the range of 20 to 120° C., separating the extract containing the polyhydroxyalkanoates from the extraction solution, and feeding the extract to a circulation loop filled with water having a temperature from 20 to 120° C. or a mixture of water and from up to 20% by weight of the extraction agent based on chlorinated hydrocarbon used for the extraction of polyhydroxyalkanoates, wherein the extraction agent is removed from this extract and polyhydroxyalkanoates precipitate.