This study was conducted to investigate the effects of impact conditions on the acoustic characteristics of a watermelon. The study was crucial to develop a device for nondestructive internal quality evaluation of a watermelon by an acoustic impulse response method. An impact device was constructed with a pendulum to hit the watermelon, a microphone to detect the acoustic impulse responses, and a digital oscilloscope and computer to store and analyze the data. The selected samples were Guemcheon cultivar watermelons(Citrulus Vulgaris Schrad) harvested on Oct. 20,1998. Sixty watermelons were tested on flour different types of sample holders, with four kinds of ball made of different materials, at four bevels of the angular position of the pendulum and distance from the watermelon to the microphone. Since the magnitudes of frequencies obtained by hitting with the steel and rubber ball were relatively small at the bandwidths of above 500 Hz, it was shown that the steel and rubber ball were not suitable far a hitting ball in the pendulum to get informations on internal quality of the watermelon. In case of using broth of the wood and acryl ball, almost the same and good acoustic responses were shown on the wide range of frequency bandwidth. Therefore, it seemed that the acryl ball was more suitable to the test than the wood ball in considering its mechanical properties. The acoustic characteristics of the watermelon were not shown a significant difference between the types of sample holder. The amplitudes of the acoustic signals and the magnitudes of frequencies from the whole samples increased with increase of the angular position of pendulum and with decrease of the distance from the watermelon to the microphone. However, the resonance resonance of the sample were almost the same regardless of the angular positions and the distances.