A technique for measuring the absolute photopeak efficiency of a 30-mm2 × 3-mm Si(Li) spectrometer in the energy region from 5 to 125 keV is presented. The measurements are made by comparing the photopeak counting rate obtained from the Si(Li) spectrometer with the respective photon emission rate using a series of absolutely calibrated γ-ray sources. A simple procedure to obtain an accurate relative efficiency curve is also given. This alternate procedure measures the relative efficiency by using three readily available radionuclides (i.e., 145Pm, 155Eu, and 241Am) whose relative photon intensities have been measured with the Si(Li) spectrometer calibrated for absolute photopeak efficiency. In addition, the K-conversion coefficients of the γ-ray transitions from 60mCo (58.6 keV), 94mNb (40.7 keV) and 176mLu (88.4 keV) and the L-conversion coefficients for those of 192mIr (58.0 keV) and 210Pb (46.5 keV) were determined from their X-ray/γ-ray intensity ratios and their respective fluorescence yields. The values obtained for these conversion coefficients are 42.1±4.5, 995±150, 1.18±0.12, 2040±430 and 14.3±1.5, respectively.