Heat treatment is one of methods to improve material properties. Heat treated tubes are used in petrochemical industry when high strength, low cost and low weight are needed. Spray cooling could be used for heat treatment because very high cooling intensity is required. This paper deals with influence of spray cooling parameters on the material hardness. Special device was developed by Heat transfer and fluid flow laboratory for quenching of small samples. Four different materials were tested. The main object of these tests was to find the influence of cooling distance, material and two-side cooling on material hardness. Device Innovatest Nexus 4303 (Vickers) was used to measure hardness in various depths from the cooled surface. Results showed that the hardness was improved for all of four materials. The influence of the spray cooling distance was not so significant. Hardness of material also depends on the cooling intensity in the inner side of the tube. If the cooling intensity in the inner side of the tube is much lower than external, it has negligible effect on the final hardness. If the inner and external cooling intensity is the same it causes increase of the hardness.