The transcription levels of the granule-associated phaP and phaR genes in Ralstonia eutropha were regu- lated through the transformation of the phbC genes from R. eutropha and Alcaligenes latus into the poly--hydroxybutyrate synthase-negative mutant. The granular morphogenesis of short chain length, poly--hydroxyalkanoate (scl-PHA) was closely associated with the mRNA transcription levels of the phaP and phaR genes, especially with the ratio of phaP/phaR genes. The phasin protein encoded by the phaP gene increased the number of granules, while the PhaR protein of the phaR gene enlarged the size of the scl-PHA granules in R. eutropha.