This document discusses ultrasonic testing of glass fiber reinforced polypropylene composites to determine the relationship between fatigue-induced strength degradation and changes in ultrasonic wave velocity and damping coefficient. Samples were subjected to oscillating bending loads and ultrasonic testing at various cycle intervals. A good correlation was found between decreasing ultrasonic wave velocity and increasing strength degradation with more fatigue cycles. Ultrasonic testing is proposed as an effective non-destructive method to assess fatigue degradation in polymer composites. Further research on other materials and loading conditions is planned.