Three rocks - biotite granite, dolerite, and marble - were studied for the use of ultrasonic pulse velocity in predicting their uniaxial compressive strength. The rocks differed in mineralogy, texture, and strength. The mineralogy and texture influence to varying degree the strength and the pulse velocity. Correlations between the compressive strength and the sonic velocity were highest in the marble (0.94-0.97), and lowest in the granite (0.68). The low correlation in the granite was attributed to the different mineral contents, the presence of biotite, the complexity in the grain boundary shape and the tortuosity of the wave path through the rock. The use of acoustic impedance and stiffness constant improved the strength of correlation in the marble but not in the dolerite and granite.