The influence of gadolinium concentration on the dynamics of deformation mechanisms in cast binary magnesium-gadolinium alloys was studied with in-situ experimental methods. Alloys were characterized by homogenous microstructure and random texture. Compression test were carried out at room temperature with simultaneously recorded acoustic emission (AE) data. Deformation test were repeated in the chamber of the scanning electron microscope (in-situ SEM). At different stages of deformation the experiment was stopped and the development of the microstructure was captured by secondary electrons and electron back-scatter diffraction (EBSD). The activated slip systems were identified in particular stages of deformation using slip trace analysis. The development of twin volume fraction was also studied. Results of AE and in-situ SEM indicate higher activity of non-basal slip systems with increasing Gd concentration. EBSD orientation maps show decreasing lateral growth of twins with higher Gd content as a result of decreased mobility of twin boundaries caused by Gd solutes. The dynamics of twinning was investigated by high-speed camera, mainly to estimate the lower limit of twin propagation rate. The results clearly indicate that the velocity of twin propagation rate is in the order of 10 m/s.