The present invention provides a recombinant microbial strain capable of stably producing a polyhydroxyalkanoic acid (PHA) at a high production rate in an industrial fermentation process. The present invention also relates to a recombinant microbial strain prepared by substituting an exogenous polyhydroxyalkanoic acid synthase gene for a polyhydroxyalkanoic acid synthase gene on the chromosome of the microorganism.