Optimum design of support materials for microorganisms is required for the construction of bioreactors. However, the effects of support materials on microorganisms are still unclear. In this study, we investigated the adhesion behavior of Escherichia coli (E. coli) on hydroxyapatite (HA), polyurethane (PU), poly(vinyl chloride) (PVC), and carbon (Carbon) to obtain basic knowledge for the design of support materials. The total metabolic activity and number of E. coli adhering on the samples followed the order of HA approximate to Carbon > PVC > PU. On the other hand, the water contact angle of the pellet surfaces followed the order of HA < Carbon < PVC < PU. The high hydrophilicity of the HA surface might be one of the suitable characters for the adhesion of E. coli. The results implied that HA has a potential as a support material for microorganisms used in bioreactors. (C) 2015 Elsevier B.V. All rights reserved.