We have synthesized the R/Ba-ordered and the R-site mixed-compound Y0.5La0.5BaMn2O6 in which (Y,La)and Ba are regularly arranged while Y and La randomly occupy the R-site.Y0.5La0.5BaMn2O6 has a tetragonal ap,× ap × 2Cp unit cell with a space group (S.G.) of P4/mmm.The temperature dependent XRD shows that the compound undergoes a structural phase transition (from tetragonal to orthorhombic) in the temperature range of 335-350K,accordingly,the magnetization exhibits an abrupt reduction at T≈340K.Those phenomena can be ascribed to the charge/orbital order (CO) transition at this temperature.Upon cooling,an antiferromagnetic(AFM) transition occurs at TN ≈180K with a moderate reduction of magnetization,and a reentrant spin glass like behavior is observed at Tf ≈50k,which may be caused by the random potential originated from the disordered A-site cations.