In this paper, the time of gas-carbonitriding effects on fatigue limit improvement of low alloy steel specimens was investigated by experimental tests of three points fatigue flexion. Besides, metallurgical evaluations and micro-Vickers hardness tests were performed employing metallographic techniques, optical, scanning electron microscopy and X-ray diffraction techniques. Test findings showed that this amount improved remarkably the components fatigue resistance. The fatigue life of carbonitrided specimens was prolonged between 16%, for CN11, and 32%, for CN21, compared to the untreated state. It is obvious, from the fractography analysis, utilizing (SEM), that fatigue cracks appeared first at the carbonitrided specimens surface.