Some properties of B_c from Lattice QCD

We discuss $B_c$ mass (1S state) and decay constant $f_{B_c}$ calculated by lattice non-relativistic quantum chromodynamcs(NRQCD) method. In leading order of $v^2$, we found that $M_{B_c} = 6.33(2)$ GeV and $f_{B_c} = 395(2)$ MeV where the error bar is the statistical error only. Using these values, we estimate QCD effects to leptonic decay width of $B_c$. The decay width is given by $\Gamma(B_c \rightarrow l^+\nu_l) = 0.86(15)m^2_l (1 - 0.0250(2)m^2_l)^2\times 10^{-14} ({\rm GeV})$, where $m_l$ is in GeV. Relativistic correction and $\alpha_s$ correction to $f_{B_c}$ have also been considered.