This paper is focused on the experimental characterization of a new class of Ultra-High- Temperature Ceramic Matrix Composites for near-zero erosion rocket nozzles. A novel test set-up has been developed to the purpose of testing small-sized samples of material in free-jet configuration, exposing them to the supersonic exhaust plume of a 200N-class hybrid rocket nozzle, employing gaseous oxygen as oxidizer and High-Density PolyEthylene as fuel. The aim of the tests was to screen the best material candidates for the final application. Two increasingly demanding test conditions have been selected. Four samples were manufactured, one based on chopped carbon fibers in a Ti3SiC2 matrix, and three based on ZrB2-SiC matrix with continuous carbon fibers. Samples surface temperatures were monitored by two-color pyrometers and an infra-red thermo-camera. In two cases, sudden jumps of temperature were detected, up to over 2800 K, associated to considerable erosion, presumably related to poor mechanical resistance of the oxidized phases forming on the exposed surface. Computational Fluid Dynamics simulations were performed in order to characterize the test conditions and investigate the material thermal behavior.