In this work the thermal relaxation method is applied to determine the specific heat of the following optical glasses: undoped chalcohalides (As2S3 and 40PbI2+30Sb2S3+30As2S3); undoped and Nd2O3 doped phosphate (38.66P2O5+40.22ZnO+21.12Na2O) and low silica calcium aluminosilicate (47.4CaO+41.5Al2O3+7.0SiO2+4.1MgO) glasses. For the latter the samples were melted both under vacuum and air conditions. Our results show that the specific heats of silica calcium aluminosilicate samples prepared under vacuum conditions were larger than that of the samples melted under air atmosphere. For chalcohalide glass sample (40PbI2+30Sb2S3+30As2S3) the occurrence of a glass transition at 171 °C was observed. These results indicate that this simple and low cost method is an useful tool to measure the specific heat of glasses as a function of the temperature.