Abstract: The experimental technique and results of ~(99m)Tc absolute activity measurementby 4πβ-γ coincidence method are described. The detection efficiency of ~(99m)Tc γrays (2.12, 140.5 and 142.6 keV) and their internal conversion electrons in 4πβcounter as a function of the VYNS foil thickness is measured. It is obtained thatafter complete absorption of 2.12 keV γ ray by the foils, the contribution fromeach ~(99m)Tc decay to the β in 4πβ counter is 0.1117±0.0005.