A sheet feeding unit and an image forming apparatus having the same. The image forming apparatus includes a body and the sheet feeding unit to supply sheets into the body. The sheet feeding unit includes a sheet feeding cassette coupled to the body, a sheet lifting plate positioned in the sheet feeding cassette to stack sheets thereon, a pick-up device to feed the sheets piece by piece from the sheet feeding plate, and an adjustment unit to vary a sheet feeding force by which the sheets are fed from the sheet lifting plate. Accordingly, the sheets can be smoothly fed into the body without skewing through adjustment of a sheet feeding force of the pick-up device.