Thermal properties of polyimides with main chain containing alicyclic units derived from 3,3' 4,4-oxy-diphthalic anhydride (ODPA) and several alicyclic-containing diamine monomers, including 1,4-bis (4-aminophenoxymethylene) cyclohexane (BAMC), 1,4-bis (3-aminophenoxymethylene) cyclohexane (mBAMC), 1,4-bis (4-aminobenzoyoloxymethyl) cyclohexane (BAZMC), and 1,4-bis (3-aminobenzoyoloxymethyl) cyclohexane (mBAZMC) were characterized in detail. The thermal stability, apparent activation energy, and evolved gas analysis of these polyimides were done using thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) spectroscopy. Experimental results indicated that the resulting polyimides showed fairly high thermal stability, no weight loss was detected before a temperature of 400 degrees C in nitrogen, and the values of glass-transition temperature of them were in the range of 134-181 degrees C. Activation energy for the initial thermal degradation of polyimide derived from ODPA and mBAMC in nitrogen were 166 and 162 kJ/mol in two different methods. The TG-IR results represented that the major evolved products from the nonoxidative thermal degradation were detected to be hydrocarbons, CO, CO2, H2O, and aromatic compounds.