In everyday life, humans always work side by side with equipment and technology which are mostly made from metal. Each metal has different characteristics, such as physical, mechanical and chemical properties. The heat treatment process aims to change the structure of the metal by heating it to a certain temperature and cooling it in various cooling media. This process has a significant impact on the mechanical properties of the metal. This research was conducted to examine the effect of variations in cooling media in the heat treatment process on the mechanical properties of ST37 material. The cooling media used are water, salt water and oil. The results showed that variations in cooling media had an effect on the hardness of the ST37 material, with salt water providing the best results in terms of balance of strength and hardness. The results of this research provide important guidance for industry in selecting optimal cooling media to improve the mechanical properties of metal materials. The results of tensile tests on the quanching process with variations of mineral water, salt water and oil gave a significant influence resulting in a tensile strength in the quanching of mineral water of 323.649 MPa, salt water of 389.128 MPa, oil of 394.329 MPa on the raw material of St 37 steel whose tensile strength was 408.349 MPa . Wear testing in the quanching process of mineral water 0.000276 mm³/kg, salt water 0.000238 mm³/kg, oil 0.000313 mm³/kg, slightly gives a good influence on wear resistance during rapid cooling of raw materials whose wear is 0.000332 mm³/kg. Meanwhile, hardness testing produced significant hardness strength in the quanching process with variations of mineral water 75 HRC, salt water 76.16 HRC, oil 76.17 HRC, and raw material 82.69 HRC.