Dense semicrystalline membranes of polyhydroxyalkanoates with medium change length (PHA(SCL)), polyhydroxybutyrate (PHB) and poly beta (hydroxybutyrate-co-hydroxyvalerate) [P(betaHB-co-XbetaHV)] were characterized using wide-angle X-ray (WAXS) and scanning electron microscopy. PHB membranes showed a more rugged surface than those of copolymers (0-22%HV). Properties such as swelling capacity, vapor permeability and selectivity were investigated. Swelling percentage in water-ethanol mixtures was 34% for PHB as compared to 14% for copolymers membranes. The ethanol/water selectivity (alpha(s)) of PHB was 5.8 which shows that it is more selective than copolymers. The water vapor and ethanol vapor permeability were determined by a gravimetric technique at different temperatures by static and dynamic methods. PHB permeability was 69.5 Barter at 30 degreesC and a discreet increment was observed at temperatures (30-50 degreesC). The difference in permeability between PHB and [P(betaHB-co-X%betaHV)] could be interpreted in terms of the crystallization rate, crystallite size and distribution which impact to transport properties of amorphous phase.