Magnesium (Mg) is a promising biodegradable metal offering many potential advantages over current scaffold technologies. Many studies have reported on the corrosion characteristics the Mg and its bioeffects in vitro and in vivo, but there are few studies on the biological effects of the corrosive products of Mg - the micron-size Mg particles (MgMPs). In this study, the effects of size-selected commercial MgMPs on bone turnover and macrophages were investigated in vivo and in vitro. We found that MgMPs were susceptible to engulfment by macrophages, leading to cell lysis, likely resulting from H-2 gas production. We also found that the inflammatory cytokines IL-1, IL-6, and TNF- were induced more strongly by titanium particles (TiMPs) group than by either MgMPs or control. Examination of the expression of bone remodeling markers revealed that MgMPs are beneficial for bone regeneration. Micro-CT scanning indicated that, 30 days postimplantation, unlike TiMPs, MgMPs had no adverse effect on either bone quality or quantity. We have investigated the bioeffects of micron-size MgMPs in vivo and in vitro, and our results indicate that MgMPs may promote bone regeneration without inducing inflammation. (c) 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 923-931, 2016.