The　{10-12}　twinning　activity　of　Mg-3Al-1Zn　magnesium　alloy　during　uniaxial　compression　at　room　temperature　has　been　investigated　by　electron　backscatter　diffraction.　The　results　indicated　that　the　twinning　activity　was　closely　related　with　two　angles:　one　was　the　angle　between　the　c-axis　and　the　compression　direction　and　the　other　was　the　angle　between　the　a-axis　and　the　titling　direction　in　the　basal　plane　for　a　given　relation　between　the　c-axis　and　the　compression　direction.　These　two　parameters　can　be　used　to　explain　which　twinning　variant　will　operate　under　the　given　strain　path.　For　the　grains　containing　a　single　{10-12}　twinning　variant,　the　{10-12}　twinning　variant　occurred　in　a　wide　range　of　Schmid　factor　values　(0＜　Schmid　factor　＜0.5)　and　the　Schmid　factor　rank　of　1　or　2　was　the　most　commonly　observed.　By　contrast,　for　the　grains　containing　two　{10-12}　twinning　variants,　the　{10-12}　twinning　activity　exhibited　a　stronger　orientation　dependence　and　the　combinations　of　Schmid　factor　ranks　1-3　and　1-2　were　the　most　commonly　observed.　(C)　2014　Elsevier　Inc.　All　rights　reserved.