The focal mechanisms of small (Mw < 4) earthquakes can be exploited to infer the structure and kinematics of faults and to analyze the stress field in which the earthquake occurs. Therefore, it is prominent to determine focal mechanisms of small events as accurately as possible. These focal mechanisms are most often found using P-wave first-motion polarities recorded at local seismic stations. Each observed P arrival is mapped to the orientation at which the ray left the focal sphere, and nodal planes are fit to the set of observations. This method accounts for possible errors in the assumed earthquake location and seismic-velocity model, as well as in the polarity observations. We applied this method to an earthquake occurred in 1994, Northridge-California. The results demonstrated that the solution obtained by this approach is reasonable and is improved against those obtained by previous methods.