When industrially separating and purifying poly-3-hydroxyalkanoic acid produced by a microorganism, to obtain poly-3-hydroxyalkanoic acid agglomerates having an arbitrary volume mean particle diameter with favorable productivity and with decreased amount of an organic solvent used is enabled while decreasing contaminants derived from constitutive components of cellular bodies. According to the present invention, agglomerates of poly-3-hydroxyalkanoic acid are obtained by adjusting the pH of an aqueous poly-3-hydroxyalkanoic acid suspension to fall within an acidic region.