In this study, the influence of grain size on the velocity of ultrasonic waves and ultrasonic attenuation in stainless steels was investigated. The aim of this study is to demonstrate the capability of ultrasonic techniques in the assessment of the grain size of steels. Heat treatment processes were carried out in order to obtain different grain sizes for AISI 304 stainless steel specimens. AISI 316 stainless steel specimens were produced by casting and tested in as-cast condition. Velocities of ultrasonic longitudinal and transverse waves were measured by means of pulse-echo method using contact type normal beam probes with 1 and 4 MHz frequencies. Apparent attenuation coefficient of longitudinal waves was determined at 4 MHz. Young’s modulus of the specimens was also determined. The results showed that ultrasonic longitudinal and transverse wave velocities and Young’s modulus were decreased with increasing grain size of the specimens. The apparent attenuation coefficient of longitudinal waves was increased with increasing grain size. © 2009 Inderscience Enterprises Ltd.