Currently, communication systems are widely used, where optical fiber is used as a transmission medium. In turn, decision and control of optical fiber parameters has become needfull, since these parameters have a significant impact on the quality and quantity of transmitted information using fiber-optic communication systems. One of these parameters is cut-off wavelength of the single-mode optical fiber, which determines the minimum wavelength of optical radiation at which the optical fiber supports only one propagated mode, in other words, operates in single-mode. The problem of decision cut-off wavelength of the optical fiber used in fiber-optic communication systems is quite relevant and demand, since when the optical fiber operates in multimode, its throughput decreases due to inter-mode dispersion. The article describes methods for measuring cut-off wavelength of the optical fiber. Variant of a high- precision apparatus for measuring cut-off wavelength of the optical fiber has been proposed and tested. The measurements were performed based on the reference bending technique described in GOST R IEC 60793-1-44-2013. The analysis of the accuracy characteristics of the developed apparatus is made, a quantitative assessment of the measurement error is obtained.