Abstarct: In this project the electronic and optical properties of Barium titanate (BaTiO3) were Investigated in both bulk and nanolaxyer forms.The calculation was done using Win2k code baxsed on Density functional theory by LDA and GGA approximations.For this purpose after optimization of the initial paronuters the band structure and total and partial density of state were calculated for both forms.The result shows both forms have direct band gaps but the band gap for nono laxyer (2.048 eV) is biger than bulk form Eg=1.83 eV by LDA and Eg=1.87 eV by GGA. BaTiO3 in bulk form has biger formation energy than nanolaxyer but the difference is small indicating the nano laxyer is also stable. The optical properties were also studies by calculating dielectric function, refractive and extinction coefficients, reflectivity, optical absorption coefficient and conductivity and energy eloss function.The result obtained for nano laxyer showed that the optical properties are anisotropic.