Field emission characteristics are investigated for boron nitride (BN) films deposited on Si substrates with cubic (c-)BN crystal grains. A comparative study of field emission characteristics is performed for the BN samples with and without c-BN grains. The turn-on electric fields are 7 and 18 V/mum for the BN samples with and without c-BN grains, respectively. A significant reduction in the turn-on electric field of the electron emission is found for the sample with c-BN grains. Fowler-Nordheim plots of the field emission characteristics suggest a variation in the field enhancement factor between the BN samples with and without c-BN crystal grains. It is also found that c-BN crystal grains are effective in increasing electron emission area.