The behavior of the fatigue crack under the narrow band random stress intensity factor was studied experimentally. It was found that stress intensity factor governs the fatigue crack growth rate under random load process as well as under deterministic load sequences, and the crack growth rate in the short range showed noticeable fluctuation while that in the long range was almost constant implying that Miner's rule could be applied for the crack growth provided that the constants were determined from random fatigue test. A small digital system with a micro-CPU and the associated software developed for this study was found suitable for random fatigue tests.