NOVELTY - Isolating polyhydroxyalkanoates from biomass fermented by microorganisms producing polyhydroxyalkanoates and/or from biomass containing crop-plant producing polyhydroxyalkanoates is claimed. The biomass if fermented is first inspissated by isolation from fermentation medium and polyhydroxyalkanoates are extracted into extraction agent based on chlorinated hydrocarbon, where extract is separated from obtained extraction solution and after removing extraction agent from this extract the polyhydroxyalkanoates precipitate, before the extraction of the polyhydroxyalkanoates from the biomass.    USE - The process is useful for isolating polyhydroxyalkanoates from biomass.    ADVANTAGE - The process: reduces the amount of extraction agent utilized; provides higher yields of polyhydroxyalkanoates with higher degree of purity; reduces overall operational costs; and forms smaller particles of polyhydroxyalkanoates which cannot be further disintegrated (having a diameter seven times smaller).    DETAILED DESCRIPTION - Isolation of polyhydroxyalkanoates from biomass fermented by microorganisms producing polyhydroxyalkanoates and/or from biomass containing at least one crop-plant producing polyhydroxyalkanoates is claimed. The biomass if fermented is first inspissated by isolation from a fermentation medium to at least 20% dry matter, and polyhydroxyalkanoates are extracted into an extraction agent based on chlorinated hydrocarbon, where an extract is separated from the obtained extraction solution and after removing the extraction agent from this extract the polyhydroxyalkanoates precipitate, before the extraction of the polyhydroxyalkanoates from the biomass by means of an extraction agent based an alkyl alcohol having 2-4C, which is added to the biomass in a weight ratio of biomass and extraction agent at 1:0.5 to 1:5, components of the biomass other than polyhydroxyalkanoates are extracted for 5-90 minutes at 20-120 degrees C, where the extract containing these components of the biomass is separated from the extraction solution obtained by filtration, decantation and/or centrifugation and the remainder of the extraction agent is removed from the solid phase by distillation from an aqueous solution or by stripping with water vapor or by drying, and polyhydroxyalkanoates are extracted from the solid phase thus pre-cleaned by an extraction agent based on chlorinated hydrocarbon, which is added to it in a weight ratio of biomass and extraction agent that is 1:5 to 1:20, where this extraction is carried out for 5-90 minutes at 20-120 degrees C, the extract containing the polyhydroxyalkanoates is separated by filtration, decantation and/or centrifugation from the extraction solution thus prepared, and this extract is subsequently fed or is continuously fed to a circulation loop filled with water having a temperature of 20-120 degrees C or with a mixture made from water and up to 20 wt.% extraction agent based on chlorinated hydrocarbon for the extraction of polyhydroxyalkanoates, by which means the extraction agent is removed from this extract and polyhydroxyalkanoates precipitate.