Microinterferometric tomography allows for determination of three-dimensional refractive index distributions in phase isotropic microelements. In this paper we present the measurement of the refractive index profile of the optical fibers exposed to the gamma radiation. Nuclear radiation is known to affect the guiding properties of optical fibers and it is therefore essential to characterize these effects to assess the applicability of fiber-optic technology for communication and sensing in nuclear industry. It is already well known that radiation affects the absorption of the fiber. Here, we investigated whether we could quantify the effect of radiation on the refractive index of core and cladding of an optical fiber.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.