Spreading of liquid and solid Ga over the surface of thin polycrystalline Ag film is accompanied by fast penetration of Ga through the film. The penetration process between +60°C and –10°C has likely a common mechanism with the spreading. The activation energies of the process responsible for spreading/penetration are EL = 0.3±0.05 eV and ES = 0.5±0.1 eV for liquid and solid Ga, respectively. The common mechanism is attributed to grain boundary (GB) grooving with diffusion of Ag out of the groove either via liquid Ga or along GBs in solid Ga. A possible formation of intermetallic compound between Ag and Ga is considered as the secondary process, which does not control the kinetics. The model reproduces the spreading/penetration rates that are observed, and gives reasonable estimates of the experimental activation energies ES and EL.