The paper presents tests results of research on the influence of fiber reinforcement on the compressive strength of fly ash from “Skawina” Power Plant stabilized with 3% addition of hydrated lime and cement. 5 × 10, 10 × 10, 20 × 10 and 20 × 20 mm foil strips and Fibrofor High Grade synthetic microfibers were used as a reinforcement. The results revealed that the compressive strength the of fly ash with reinforcement Fibrofor High Grade fibers was 2-times higher compared to the tests with foil strips. The compressive strength of the fly ash with the addition of Portland cement was significantly higher than with the addition of hydrated lime.