Abstract: The reference radiation and procedure for calibration of environmental dosimeters in this laboratory are presented. The total uncerntainty of conventional dose value given by MCD-100 type ionization chamber, with air-attenuation and backscattering corrected, is unlikely more than ±2.5％ for filtered X-ray, ±1.5％ for ~(137)Cs and ~(60)Co γ -radiation respectively.