Abstract: The theory and experimental method for ultrasonic moduli measurement of unidirectional fiber reinforced composite has been systematically studied in the present paper. Effects of fiber surface on the elastic moduli were measured by using ultrasonic water-tank method. The ultrasonic technique has advantages over static or low-freduence methods and all five independent elastic constants can be determined by the technique and on the same sample. The accuracy for the other stiffness constants was 3-5%.The C₁₃(cross-plane modules) were accurate to 1200.