To evaluate the potential of polyester-based ionomers as biomaterials, we have characterized them in terms of crystallization behavior, degradation, and in-vitro cellular interactions. The polymers used are poly(butylene succinate)-based ionomers (PBSis) with 1 to 5 mol-% dimethyl 5-sodium sulfoisophthalate. Even a few incorporated ionic groups significantly decreases the folding surface energy, indicating that folding into crystalline lamellae is more difficult for chains restricted by ionic aggregates. Transmission electron microscopy (TEM) does not reveal any distinct aggregation of ionic clusters following hydrolytic degradation, which suggests that the physical crosslinkage due to ionic interactions is vulnerable to hydrolysis. The in-vitro cellular interactions of polyester-based ionomers is assessed by the culture of human dermal fibroblasts with PBSi extracts or in direct contact with the PBSi films. Cells on PBSi films and in their extracts exhibit appropriate specific growth rates and normal metabolic function regardless of the incorporated ionic content compared with poly[(D,L-lactic acid)-co-(glycolic acid)] (75:25, PLGA), which is well known to be biocompatible. The cells growing on PBSi films spread to a sufficient extent, displaying relatively active filopodial growth, as compared to that of parent PBS. These results suggest that the conspicuous topology and hydrophilic nature of the ionomer surface affect cellular interactions, and that this ionomer therefore has potential applications as a biomaterial.