The stress relaxation phenomena in magnesium alloys, containing Al, Sr and Ca solutes have been investigated. The samples were deformed at a constant initial strain rate at various temperatures between room temperature and 300 °C. Stress relaxation, i.e. a decrease in the stress with time, was measured at various stresses and at various temperatures. The stress relaxation curves were analysed as a function of the internal stress at the beginning of the relaxation and the test temperature.