The in vitro degradation of magnesium (Mg) alloys containing low levels of strontium (Sr, 0.05, 0.1 and 0.2 wt%), with and without addition of zinc (Zn, 0.5 and 1.0 wt%), was studied for potential use in orthopaedics for fracture treatment. Alloying Mg with Sr was selected as a promising strategy to utilise the biological effect of Sr in inducing accelerated bone tissue growth. The influence of controlled alloying upon degradation rate was studied via electrochemical measurements and immersion tests in minimum essential medium (MEM). Immersion testing revealed a comparable degradation rate of the alloys tested herein, indicating no detrimental effect of Sr on degradation. Cytotoxicity experiments on primary mouse osteoblasts indicated good biocompatibility and enhanced proliferation of osteoblasts for all the tested Mg alloys. Potentiodynamic polarisation testing further confirmed that addition of low-levels of Sr had a minor influence on cathodic kinetics, with a slight inhibition of anodic kinetics. In contrast, the addition of Zn as a ternary element moderated both anodic and cathodic kinetics of Mg–Sr alloys.