The major crystalline phases in magnesium oxychloride cement (MOC) have been extensively studied, but the other phases have not been studied due to the difficulty in identifying them. In the current study, we focused on the effect of chlorine-containing phases other than crystalline oxychlorides on the strength of cured MOC materials. The alcohol leachable chloride (ALC) was proposed to characterize the other phases containing chlorine, and the absolute ethanol leaching test was developed to determine ACL content in a cured MOC paste. The results showed that either decreasing MgO/MgCl(2)molar ratio or increasing H2O/MgCl(2)molar ratio led to an increase in ALC content in cured MOC slurry, but adding a small amount of phosphoric acid resulted in very little or almost no ALC in the modified MOC slurry. In addition, increasing ALC content has been shown to significantly reduce the compressive strength of hardened MOC pastes. Thus, the modified MOC pastes had high strength, compared with the corresponding common MOC pastes. According to the experimental results, the relationship between the ALC content and the compressive strength of cured MOC materials was established. Therefore, a low ALC content was proposed as a characteristic index of high-quality MOC materials.