Mg-based foam biomaterials were prepared by a melt foaming process, wherein a Mg-Ca alloy was used as the matrix material, hydroxyapatite (HA) as the tackifier, MgCO3 as the foaming agent. The Mg-based foam biomaterials with uniform structure were tested to investigate their biodegradable behaviors. The biodegradable property of the Mg-based foam was mainly characterized by microstructure observation, immersion tests and electrochemical measurements. The results show that the weight loss rate increases with the increasing porosity of the specimen over a fixed period of time. The weight loss rate of the specimen without HA particles is much higher than that of the specimen with HA particles. Meanwhile, the open porosity of the Mg-based foam biomaterial increases with immersion time. Both the total porosity and added HA content have an important impact on the open porosity of the Mg-based foam biomaterial. Over a fixed period of time, the open porosity of the Mg-based foam biomaterial increases with the increase of the total porosity. Mg-based foam biomaterials with added HA exhibit higher corrosion resistance than Mg-based foam biomaterials without HA in simulated body fluid (SBF) media.