High crystalline Ti-substituted MCM-41’s in the range of Si/Ti ≥ 30 were synthesized. We have carried out the controlling of the pore size of highly crystalline Ti-substituted MCM-41 simply by varying the synthesis temperature in 100-165 oC range. Depending on the reaction temperature, highly crystalline Ti-substituted MCM-41 with different d100 values in the range of 34.6-55.8 Å while using the same gel mixture (1.0 SiO2 : 0.27 CTABr : 0.19 TMAOH : 0.017 Ti(OEt)4 : 40 H2O) were synthesized. The pore size distribution, the surface area and the wall thickness for Ti-substituted MCM-41 samples by N2 adsorption method were 29.2-35.8 Å, 1140- 959 m2/g and 10.7-28.7 Å, respectively. Ti atoms substituted in MCM-41 were atomically dispersed in the framework of MCM-41, which was investigated by IR and UV/Vis spectrophotometer. The d100 values of Ti-MCM-41 samples of Si/Ti=30 under same reaction have a range of 39.2-53.5 Å.