Effect of grain size and inclusions on tensile strength and the Charpy V-notch impact absorption energy of HY180 steels has been investigated by means of optical microscopy, energy dispersive X-ray spectrometry, scanning electron microscopy, tensile tests and Charpy V-notch impact tests. Grain growth during austenizing treatments in Ti-modified alloy was smaller than that in Ti-unmodified alloy. and consequently Ti addition was very effective to grain refinements of HY180 steels. Inclusions containing Ti and S were formed in Ti-modified alloy, while MnS in Ti-unmodified alloy. Tensile strength decreased with raising austenizing temperature, which was attributed to the grain growth. The Charpy V-notch impact absoprtion energy of Ti-unmodified alloy increased with rasing austenizing temperature, while it kept almost constant in Ti-modified alloy, although grain size of the alloy increased.