The efficiency and calibration curves as function of gamma- ray energy for a germanium detector are usually established by using many standard gamma-ray sources of radionuclides decaying with few gamma rays or radionuclides having complex decay scheme, as 152 Eu or 133 Ba. But these radionuclides cannot be used alone, because they have a few gamma lines with high intensity and these lines have a irregular distribution in the energy spectrum. 166m Ho is found to be a convenient single source for such calibration, because it decays by b - with subsequent emission of about 40 strong and well distributed gamma lines between 80 and 1500 keV. Moreover, its long half - life (1200 years) and X-rays characteristics between 40 and 50 keV makes it a good standard for calibration of germanium detectors. However, it is necessary to know with accuracy and precision the gamma ray intensities of their main lines, due to the fact that literature has showed discrepant values. Then, a methodology to determine the emission probability of its main lines is proposed by means of combined use of gamma spectrometry and coincidence 4pb - g techniques. The experimental results show consistence to the others authors, with lower or compatible uncertainties.