The effects of sintering temperature on the surface roughness of gypsum bonded investments were investigated to find the appropriate sintering temperature applied for micro-investment casting. The surface roughness tests were carried out at sintering temperatures ranging from room temperature to 1,000 ℃for investment compounds mixed from calcium sulphate α-hemihydrate and quartz powder (wt.%, 6:4; 5:5, 4:6, 3:7). In this experiment, each investment compound was prepared by pouring the investment materials into a plastic bottle with the good surface roughness (Ra ～0.2 urn). DTA-TG curves were measured using a thermal analyzer to investigate the difference of surface roughness at different temperatures. The results show that the surface roughness of gypsum bonded investment is temperature sensitive. The preheating temperature of the mold should be up to 600 ℃, but not over 700 ℃, and the investment compound with 60 % plaster and 40 % quartz powder is applicable for preparing the micro-structures. The micro-structures with 100 Mm diameter were produced in the present studies. The results show that the surface roughness of the casting is only Ra ～0.51 urn, slightly rougher than that of the investment mold.