Calcium phosphate ceramics constructed from beta-tricalcium phosphate (TCP) and hydroxyapatite (HAP) have been successfully used as implant materials. However, there is a possibility that these materials are responsible for an unwanted inflammatory response during wound healing. Since TCP is soluble in the body, the instability of this material may contribute to this inflammatory response. Using composite ceramics of TCP and HAP that possessed Ca/P molar ratios of 1.50, 1.55, 1.60, 1.64, and 1.67, the effect of surface instability on fibroblast L-929 cells was investigated. The time-dependent variation of the initial anchoring ratio, cell density, and cell viability were measured. In general, the cells were severely damaged and ruptured on the highly soluble thin surface layer of the TCP-HAP ceramics. The initial anchoring ratio for TCP-HAP ceramics was as high as that for the polystyrene dish (Lux, control). However, viability at 6 h decreased to less than 50% of the initial cell density on ceramics with a Ca/P molar ratio of 1.64 (20% TCP-80% MAP), while 85% of the cells were viable on Lux. The viability on 100% TCP, whose surface is the most highly soluble among the TCP-HAP ceramics used in this study, was reduced to 20%. Morphological observation showed that the anchored cells were ruptured when grown in culture medium on the 100% TCP. Although the high solubility of the thin surface layer on the TCP-HAP ceramics of the carrier was found to be the dominant factor in the decreasing cell viability, the initial viability was enhanced by the stabilization of the surface of the TCP-HAP ceramics by pre-incubating the scaffolds in a culture medium containing 10% fetal bovine serum for 3 d.