Optical system for controlling the unbroken condition of warp yarns in a weaving loom wherein on optical reading device is apt to detect a continuous succession of images of the warp yarns as a whole, or of a subset of the same, and a processing unit (U) is apt to measure in a continuous manner one or more parameters of each of said images. The processing unit (U) sends a stop command to the loom and an eventual alarm signal when one of said parameters relative to the last acquired image differs, by a pre-established quantity, from a predetermined value of said parameter or from the value of such parameter measured in one or more of the images preceding the last acquired image.