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In the present paper the effect of surface roughness in the amplitude of the ultrasonic signal was analyzed. The method of pulse-echo was used by direct contact in order to conclude the presence of flaw detection. Steel samples AISI/SAE 1038H with roughness of 0.34pm, 4.67 pm, 11.34pm and 23.92 pm were used. The back surface roughness of all specimens was kept constant at 1.5 pm Ra by grinding operation. 1.5, 2, 3, 4 mm. holes were drilled at constant depth and to same side of each specimen to represent reference reflectors at frequencies of 2.0 and 4.5 MHz’s. Best signals of reflectors were attained at the frequency of 4.5 MHz in steel samples. From the test results, it can be seen that the attenuation of the signal depends on the surface roughness. The analysis of the spectrum of the signals displays that attenuation increases with the surface roughness. Though there was no uncertainty observed about not being able to detect discontinuity because of roughness but the correct couplant and frequency choice has a positive effect on correctly sizing the discontinuity and at attenuation measurements.