In order to investigate the effect of comonomer-unit composition and its distribution of bacterial poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] on the miscibility of its blend with poly (ethylene oxide) (PEO), as-bacterially synthesized and well-fractionated P(3HB-co-3HHx)s with different 3HHx unit content were blended with PEO at different content. It is found that the miscibility between P(3HB-co-3HHx) and PEO decreases dramatically with increasing both 3HHx unit content of P(3HB-co-3HHx) and PEO content in the blend. The miscibility is also found to be significantly affected by the comonomer-unit compositional distribution of P(3HB-co-3HHx). Strongly depending on the comonomer-unit composition of P(3HB-co-3HHx) and PEO content in the blend, thermal stability and mechanical properties of P(3HB-co-3HHx) can be regulated by blending with PEO. Moreover, PEO exhibits good dispersion in P(3HB-co-3HHx) matrix. It is concluded that the P(3HB-co-3HHx)/PEO binary blend can exhibit diverse properties by varying the comonomer-unit composition and comonomer-unit compositional distribution of P(3HB-co-3HHx) as well as the PEO content in the blend. (C) 2010 Elsevier Ltd. All rights reserved.