Recently, much attention has been paid to the application of tissue engineering technology to bone regeneration. Bio-polymers such as collagen and bioactive ceramics such as hydroxyapatite and tricalcium phosphates are used as raw materials for the scaffolds for in vitro regeneration of bone tissue. These materials have been used to develop the scaffolds independently but also polymer-ceramics or polymer-polymer composites have been considered as advanced scaffolds having mechanical stability, biocompatibility, cell proliferation and easy processability. However, the relationship between the mechanical properties and the cell proliferation behavior of those composite scaffolds has not been clarified yet. In this study, two different types of composite scaffolds such as PET fiber/collagen and β-TCP/gelatin scaffolds were investigated. MC3T3-E1 cells were cultured in these scaffolds under appropriate condition. Compression tests were then conducted periodically by using a conventional testing machine to evaluate the compressive elastic modulus. It was found that the modulus of the scaffolds with cells increased with increase of the cell culture period. It is noted that the modulus of the β-TCP/gelatin with cells was about seven times larger than the PET fiber/collagen with cells. This result clearly showed that the proliferation ability of MC3T3-E1 cells is effectively improved under the existence of β-TCP. The structures of the scaffolds with proliferated cells were also characterized using a field emission scanning electron microscope (FE-SEM). The FE-SEM results clearly exhibited that β-TCP/gelatin has better ability for cell proliferation than PET fiber/collagen. Effectiveness of β-TCP for bone tissue regeneration was thus confirmed in this study.