During fatigue phenomenon, cyclic loading causes a material to fail prematurely and suddenly like a brittle failure at a stress level less than determined strength under monotonic condition. It is reported that 90 percent of mechanical failure in other materials are caused by fatigue. Rock formations and structures, such as tunnel walls, excavation roofs and ribs, rock columns, bridge abutments, dam and road foundations and also underground spaces like compressed energy storage system, could be subjected to cyclic loading resulting from different sources such as vibrations of the earth’s crust, through major earthquakes, rock bursts, rock blasting and drilling and also, traffic. The reaction of rocks to cyclic and repetitive stresses has been generally neglected with the exception of a few rather limited studies. But fatigue failure might be very important in rock structures because of natural defects, fractures, and cracks in the rock mass. In this research, the behavior of five different rocks under bending cyclic loading is evaluated. For this purpose, a new apparatus is developed based on the rotating beam fatigue testing machine (R.R.Moore), which is commonly used for laboratory fatigue test in metals. The results obtained from five frequently used quarry stones with different formations, and mineral composition shows that for all rocks the number of cycles that a specimen withstood before the failure (the fatigue life) was increased by decreasing the stress level. The obtained results (S-N diagram) followed common stress- life relationships including W?hler relation, Basquin relation, Stromeyer law, and Weibull relation; but the “W?hler relationship” is the best-fit relation for intact rocks. In addition, results showed that all rocks have an endurance limit. The endurance limits for all rocks are obtained in the range of 0.4 to 0.6 of their static tensile strengths between 1 to 10 million cycles. Correlation tests noted that the best agreement between endurance limit and a mechanical strength parameter is that obtained with the ultimate tensile strength under bending. The relationship between the endurance limit of intact rocks and the ultimate tensile strength under was a quadratic relationship in the form of Brand and Sutterlin formula. The results showed that the fatigue life improves with increasing the loading frequency, that the loading frequency does not influence the fatigue limit. The observed failure section of rock samples showed two domain: a smooth and wavy band feature in fatigue failure part and the failure face was completely rough, showing a sudden failure condition during the final stress cycle. Separation of grains and powdering in failure surface of fatigue fracture is clearly more than the static failure. Results showed that the effect increasing the amount of midrange stress (either tensile and compression) reduce the fatigue limit of intact rocks. The relationship between the fatigue limit of intact rocks and the midrange stress is in agreement with Modified Goodman line. The results obtained in this research confirmed that the stress-life method and developed apparatus are suitable for studying fatigue phenomenon in rocks.