Abstract: The experimental studies on frictional sliding of four kinds of rocks were made by the double shear test method. The samples were made of Jinan gabbro, Dianchangshan marble, Zhoukoudian limestone and Xiaolangdi sandstone. The applied normal stresses a in experiments range from 20 to 60 MPa. Under these normal stresses in experiments on gabbro the stick-slip happened. When σ = 20MPa the displacement weakening was observed. When σ = 40MPa and σ =52.5MPa the friction strength was kept cconstant in process of stick-slip. When σ =57MPa the displacement hardening was obserTed. For marble and sandstone when σ=20MPa the stable sliding happened. When σ=40MPa the stick-slip happened and the displacement weakening was observed. For limestone no stick-slip was observed. The friction between gabbro and marble exhibited stick-slip with visible displacement weakening. The friction strength is lower than that of Byerlee's law except sandstone. In the case of displacement hardening, the premonition of AE before stick-slip is quite obvious while for displacement weakening, the case is opposite. The nature of displacement hardening and displacement weakening are analyaed. The meaning of study on friction of rocks is discussed.