Nitrogen-doped 6H-SiC single crystals were grown by the modified Lely method (the sublimation method). The crystallinity and electrical properties of the grown crystals were investigated through optical absorption measurements, Hall measurements (van der Pauw method) and etch pit measurements (the molten alkaline etching method). Nitrogen gas was introduced into the furnace with a partial pressure of 0.05-0.8 Torr during the crystal growth. The nitrogen concentration in the crystals increased with the nitrogen partial pressure. The etch pit density (EPD) increased as the nitrogen concentration increased. The increase in the number of etch pits was ascribed to the increase in rows of edge dislocations (subgrain boundaries). It is suggested that the nitrogen incorporated in the crystal might trigger the generation of subgrain boundaries. It should be noted, however, that the amount of doped nitrogen did not affect the micropipe densities (MPD: ~1cm^-2). A 6H-SiC wafer (12 mm in diameter) with resistivity as low as 0.03Wcm was obtained with relatively low defect densities (MPD: 1 cm^-2, EPD: 4.5x10⁴ cm^-2).