Sputtering deposition of LaB6 thin film was developed, and work function of the sputtered LaB6 film was investigated. It was found that the work function depends greatly on the nitrogen and the oxygen concentrations in the LaB6 sputtering target. Low work function of 2.4 eV was obtained in the case of nitrogen concentration of approximately 0.4%. At the same time, the oxygen concentration must be less than 1% to obtain low work function. In this condition, the it was found from the Hall measurement results that the sputtered LaB6 film exhibited both the highest electron mobility (1.5 cm2/Vs) and the highest electron density (3.3×1022 cm-3), suggesting that orderliness between atoms was improved at this condition, resulting in the realization of low work function.