We report experimental demonstration of a magneto-optical trap (MOT) of Rb atoms with a high optical density. With 2.2-cm-diameter cooling laser beams, we achieve an optical density of nearly 11 for about 2.6 × 1010 trapped Rb atoms with the beam intensity of about 6.6 mW/cm2 per beam. The temperature of the cold atoms is about 250 μK. Furthermore, by ramping the magnetic field gradient from 8 G/cm to about 20 G/cm, the atomic cloud in the MOT is compressed and the optical density is up to 16.