Mn-substituted $BiFeO_3$(BFO) thin films were prepared by r.f. magnetron sputtering under an Ar/$O_2$ mixture of various deposition pressures at room temperature. The effects of the deposition pressure and annealing temperature on the crystallization and electrical properties of BFO films were investigated. X-ray diffraction patterns revealed that BFO films were crystallized for films annealed above $500^{circ}C$. BFO films annealed at $550^{circ}C$ for 5 min in $N_2$ atmosphere exhibited the crystallized perovskite phase. The (Fe+Mn)/Bi ratio decreased with an increase in the deposition pressure due to the difference of sputtering yield. The grain size and surface roughness of films increased with an increase in the deposition pressure. The dielectric constant of BFO films prepared at various conditions shows $127{sim}187$ at 1 kHz. The leakage current density of BFO films annealed at $500^{circ}C$ was approximately two orders of magnitude lower than that of $550^{circ}C$. The leakage current density of the BFO films deposited at $10{sim}30;m$ Torr was about $5{ imes}10^{-6}{sim}3{ imes}10^{-2}A/cm^2$ at 100 kV/cm. Due to the high leakage current, saturated P-E curves were not obtained in BFO films. BFO film annealed at $500^{circ}C$ exhibited remnant polarization(2Pr) of $26.4{mu}C/cm^2$ at 470 kV/cm.