The lasingin an Nd:YAG laser with a fiber-optic reflector in the form of a loop was experimentally investigated. Two designs of the laser with a fiber-optic loop reflector were considered. In the laser of the first type the reflector was formed by a fragment of a fiber guide the ends of which were placed in the focal plane of a microscope objective. In the laser of the second type the role of the output mirror was played by a loop-shaped fiber-optic reflector made on the basis of a V-shaped fused three-fiber splitter. It is shown that when such lasers operate in the regime of free-running lasing, in them there takes place the effect of nonlinear conversion of the generated radiation frequency in the Stokes and anti-Stokes regions of the spectrum.