The effect of surface adsorbates on splat formation during thermal spraying is examined by controlling substrate adsorption.Splats are formed on a polished flat stainless steel substrate surface by plasma spraying. The adsorption state of the substrate iscontrolled with different organic substances of different boiling points and different preheating temperatures. The droplet materialsused are aluminum, nickel, and Al O 2 3. Three kinds of organic substances used are xylene, glycol and glycerol, which are brushedon the surface of the substrate before spraying. It is revealed that when preheating temperature of the substrate is lower than theboiling point of the organic adsorbates on the substrate surface, the splashing occurs during droplet flattening which results in theformation of the splats with an irregular morphology. However, when the preheating temperature exceeds approximately 50 8Cover the boiling point of the organic adsorbates and evaporates all organic substance adsorbed on the surface, the regular disktype splats are formed which corresponds to no occurrence of the splashing during splatting. It is clearly shown that the existenceof the evaporable adsorbates on the substrate surface influences significantly the splatting and consequently the splat morphology.On the basis of the result, the evaporated-gas-induced splashing model is proposed to explain the occurrence of splashing duringsplatting of a spray molten droplet and the formation of the reduced splat. The effect of preheating temperature of a substrtaesurface on water adsorption and desorption characteristics in ambient atmosphere is disscussed from the point of view to create aclean surface and regular disc splat.