Interferometric fiber optic sensors (FOS) are often used for the nondestructive precision measurement of wide spectrum of physical units such as temperature, pressure, acoustic and electromagnetic fields. Their pinpoint accuracy and high dynamic range are aptly combine with unique advantages of fiber optic element base. One of the most essential factors, limiting sensitivity of such sensors is noise of radiation source (laser). Thought for design and development sensors it is necessary to know a spectrum of laser noise in the range of measured influences. Noise features of semiconductor lasers are sufficiently well known. Gas lasers, by reason of their high coherence, are often used in interferometric FOS. However, information about their amplitude noise spectrum is relatively little. In given work are shown results of intensity noise measurements for serially produced small-size gas lasers, suitable for FOS. Besides, sensitivity can be greatly affected by increasing of noise, caused by the light, reflected back in the laser from different optical components of scheme. For this reason in work are brought measurements results of influence back-reflected light upon amplitude noise of laser.