Research in “Heat Treatment effect on Rod Steel AISI 1045 and AISI 4140”. This book is mainly covered the effect of heat treatment and continuous cooling treatment on two types rod steels, AISI 1045 and AISI 4140. Specimens were heated until 950°C and soaked for three hours in furnace. Then the specimens was cooled at different rate as indicated such as furnace cooled, air cooled, blowing air cooled, oil quenched, and water quenched. Hardness test, compress test and observed microstructure were performing on steels by using Rockwell Hardness Test, Universal Testing Machine and Scanning Electron Microscopy. By using water and oil quench, results will shows the hardness of the steels is increased after heat treatment. Continuous cooling treatment at different rate on steels will results formation of the martensite and decomposition of the microstructure.