The purpose of the present invention is to provide a method for enhancing the production quantity of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HH)) having a high fraction of 3-hydroxyhexanoate (3HH) using a saccharide or glycerol as a starting material. The present invention provides: a method for producing a P(3HB-co-3HH) copolymer including performing transformation by homologous recombination of a crotonyl-CoA reductase gene in a chromosome of a recombinant strain of Cupriavidus necator endowed with the ability to produce P(3HB-co-3HH), or performing transformation by introducing an autonomous replication vector in which the crotonyl-CoA reductase gene is incorporated in the aforementioned strain, and cultivating the transformant in a medium containing a saccharide or glycerol as a carbon source; and a method for enhancing the production quantity of the copolymer and/or the fraction of 3HHx in the copolymer.

Provided are a method for enhancing the production quantity of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HH)) having a high fraction of 3-hydroxyhexanoate (3HH) using a saccharide or glycerol as a starting material; a method for producing a P(3HB-co-3HH) copolymer including performing transformation by homologous recombination of a crotonyl-CoA reductase gene in a chromosome of a recombinant strain of Cupriavidus necator endowed with the ability to produce P(3HB-co-3HH), or performing transformation by introducing an autonomous replication vector in which the crotonyl-CoA reductase gene is incorporated in the aforementioned strain, and cultivating the transformant in a medium containing a saccharide or glycerol as a carbon source; and a method for enhancing the production quantity of the copolymer and/or the fraction of 3HHx in the copolymer.