In the present work, we studied the twinning-detwinning (TDT) behavior of E-form Mg alloy (EFMA) sheets during cyclic loading-unloading via in-plane compression and in-situ tensile tests, respectively. An in-plane compression test was conducted to induce pre-twinning in order to tailor the initial texture of an EFMA sheet. Detwinning kinetics of EFMA was linked to both crystallographic orientations and the morphology of twin bands. EBSD results indicated that most of the pre-twins were removed at lower tensile strains (0.04-0.06) during the in-situ tensile test. The thickness direction strains were effectively accommodated via the detwinning of twin bands in the pre-twinned EFMA sheet under lower tensile strains. Under higher tensile strains (0.08-0.12), however, the deformations were accommodated via the dislocation accumulation in localized deformation regions, which resulted in relatively higher average KAM (kernel average misorientation) and GOS (grain orientation spread) values at the grain and twin boundaries (TBs) during in-situ tensile testing. Resolved shear stress (RSS) analysis and a crystal plasticity finite element method (CPFEM) were used to investigate the detwinning behavior during in-situ tensile testing. The rate of detwinning showed a linear relationship with both the average RSS for twin bands and the average accumulated detwinning fraction when multiplied by the real average twin width. © 2019 Elsevier Ltd.