Rock formations, as well as rock structures, are subjected to both static and dynamic loads. Dynamic forces are intermittently applied through earthquakes, rock bursts, rock blasting, drilling and traf?c. Mechanical properties of rocks under dynamic loading condition are obviously different from static loading condition. In recent rock engineering designs, greater attention is focused on the behaviour of rock in dynamic loading, fatigue loading (cyclic loading), under varying strain-rate conditions, and in the post-failure state. The study of rock behaviour under dynamic conditions is of special interest since the diverse dynamics signi?cantly in?uence rock properties. It i know that different materials show different responses under dynamic loading conditions. Some of these material become stronger and more ductile, while other become weaker and more brittle. Better understanding of cyclic fatigue in dynamic loading conditions could assist planners i preparing a more rational design that would eliminate remature failures. It could aid i earthquake, rock burst prediction and control research. Knowledge of fatigue characteristics could also help improve rock-breaking methods. In the literature there are a few works on evaluating the behavior of rocks under compression cyclic loading. During the past few years, considerable efforts have been made to study the response of rock to cyclic loading. It was reported that the fatigue properties of rock material were dependent o the maximum stress, amplitude, loading waveform and frequency, etc. In this research work the behavior of rocks under completely reversed loading condition (tension-compression) has been investigated by developing a new apparatus based on commonly laboratory fatigue test in metals. A set of laboratory experiments have been conducted on two crystalline marble rocks (maroon and green marble) with two different grain sizes and fatigue phenomenon are determined. Rock sample size were 11 mm diameter and 120 mm length. Totally Eighty samplefromtwotypeof rockwas prepared and Seventy fatigue testwere carried outin this research work and thefatiguecurvewerelottedforeachtypeof rock. Also the endurance limit may be detected which cannot be determined in ordinary cyclic loading tests on rocks in previous works. It Can be seen that the crystalline rocks in special the stress range under cyclic loading remains stable and are not broken ,therefor we can say that this type of rocks have endurance limit. The obtained stress endurance limit range for maroon marble and green marble are (4-6) Mpa and (7-10) Mpa respectively. The results show that there is a great influence of grain size on fatigue behavior of rocks. With increasing the grain size the rock becomes more liable to fatigue crash. Also fatigue strength of maroon marble is more scattered than the green marble mainly due to the anisotropy effect in mechanical properties of maroon marble.