YMnO3 thin films were prepared on Pt/Ti/SiO2/Si substrate by chemical solution deposition method. The films were crystallized by heat-treatment at 85$0^{circ}C$ for 1 hour. Effects of an annealing atmosphere(O2, Ar, vacuum) on the crystallization behavior and electridcal properties were investigated. YMnO3 thin films annealed under Ar atmosphere showed a superior crystallinity and a very strong c-aix preferred-orientation which was a polar axis. Leakage current density of the films decreased with lowering oxygen partial pressure of the annealing atmosphere. C-V and P-E ferroelectric hysteresis were observed only in the thin film heat-treated under Ar atmosphere.In order to prepare YMnO3 thin films having both low leakage current and ferroelectricity, the annealing atmsphere should be kept under a proper oxygen partial pressure which was about 1 Pa in this work. Leakage current density at 1 volt, dielectric constant($varepsilon$r), remanent polarization(Pr), and coercive field(Ec) were 1.7$ imes$10-8 A/$ extrm{cm}^2$, 25, 1.08$mu$C/$ extrm{cm}^2$, and 100 kV/cm, respectively.