The cellular responses to polyhydroxyalkanoates (PHA) degradation products oligo-hydroxyalkanoates (OHAs) are very important factors that control the biocompatibility of these polymers when they are used in tissue-engineering applications. In this study, oligo (3-hydroxybutyrate) (OHB, Mn 2000), oligo(3-hydroxybutyrate-co-4-hydroxybutyrate) (O3HB4HB, Mn 2100, 6 mol% 4HB), oligo (3-hydroxybutyrate-co-3-hydroxyhexanoate) (OHBHHx, Mn 2800, 12 mol% 3HHx) and medium-chain-length oligo(3-hydroxyalkanoates) (OmclHAs, Mn 2300, 2 mol% 3-hydroxyhexanoate (3HHx), 25 mol% 3-hydroxyoctanoate, 71 mol% 3-hydroxydecanoate and 3 mol% 3-hydroxydodecanoate) were prepared as insoluble particles in aqueous solution. Liposomes were employed to encapsulate OHAs and facilitate their transfer into the cytosol. The methylthiazol tetrazolium (MTT) assay, a cell apoptosis study and the flow cytometry were used to evaluate cell viability of mouse fibroblast L929. OHAs in concentration lower than 20 mg/l did not significantly affect cell viability, while OHAs over 40 mg/l reduced cell viability with more cell apoptosis, more cell death, delayed cell cycle and reduced cell proliferation. The cytotoxicity of OHAs decreased with increasing OHAs side chain length. It is proposed that medium-chain-length OHAs containing PHA, such as poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and medium-chain-length PHA Poly(3hydroxyalkanoates) (mcl PHA), are preferred for development and application as PHA-based tissue-engineering biomaterials.