Mechanical surface treatment has been applied in 304 stainless steel. To reveal its effect under chloride solution droplet, the surface potential distribution was conducted using scanning Kelvin probe observation method. The surface potential distribution was done with and without droplet electrolyte on the surface of the samples. To clarify the corrosion product and rust, microscopic observation was conducted in the tested material. In this study, MgCl2 solution was employed as droplet electrolyte due to its deliquescence in the atmospheric environment. The investigation process was applied at 40% RH. It was observed that the surface potential of the treated sample transformed into more noble. Moreover, the pit did not form in the treated sample unlike in the untreated sample.