Although the Gd5Si4 alloys exhibit the second-order phase transition and the large magnetic entropy change in the near room temperature, its Curie temperature is single. To search the new magnetic refrigeration materials which Curie temperatures are tunable in the range of near room temperatures, the authors of this paper researched on the crystal structure and the Curie temperatures of (Gd1-xDyx)5Si4(x=0.1, 0.2, 0.3, 0.35) and (Gd1-xHox)5Si4(x=0.05, 0.15, 0.25) alloys that were prepared by arc melting in an argon atmosphere. The vacuum heat treatment of the alloys was carried out at 950℃ for 168 h. X-ray diffraction patterns reveal that orthorhombic Gd5Si4-type structure remains unchanged. The lattice parameters, cell volumes, and x-ray densities were estimated using the Rietveld method. It shows that the lattice parameters decrease gradually in the (Gd1-xREx)5Si4(RE=Dy, Ho) alloy system with increasing Dy or Ho concentration. The results of magnetization versus temperature experiment show the Curie temperatures of (Gd1-xREx)5Si4 systems are tunable continually from 336 K to 260 K and the desired Curie temperature can be obtained with the different RE content. It was found that the Tc3 of the alloys decrease almost linearly with increasing x. As a result, a formula used to estimate the Curie temperature was obtained.