Polyhydroxyalkanoates (PHAs) are biopolymers  accumulated in a number of  microorganisms as carbon and energy storage materials under the nutrient-limiting condition in the presence of an excess carbon source. PHAs are considered to be one of the potential alternatives to petrochemically-derived plastics due to their versatile material properties. Unlike short chain length (SCL) PHAs, medium chain length (MCL) PHAs possess a much lower crystallinity and higher elasticity. With the effort of improving MCL PHA production, a number of studies have been carried out for the past few decades. However, MCL PHA production is still economically poor in order that it is able to be brought into a practical application. In this study, by introducing yeast β-oxidation pathway into different mutant E. coli , we obtained an improved amount of MCL PHA produced in fadAB mutant E.coli strain (WAB101) and fadR atoC (Con) mutant E.coli strain (LS5218) which produced MCL PHA 1.5 and 7 times as much as did the control strains, respectively. In addition, it is the first time that eukaryotic system has been introduced into prokaryote for MCL PHA production.