Gravimetrically the corrosion of mild steel was studied in water and different water based acid solutions like 0.1 M HCl, 0.01 M citric acid, 1:1 volume ratio of 0.1 M HCl & 0.01 M citric acid. The corrosion studies were analysed in terms of first order kinetics of the steel where water was found very mild corrosive medium as the corrosion rate constant was found 8.0661 × 10-4 g/day. 0.1 M HCl was recognized to possess highest corrosion rate constant of 3.3866 g/day among the four mediums. The unexpectedly high corrosion of mild steel in 0.01 M citric acid-water medium was explained in terms of possible solubilisation of iron hydroxide. The presence of [citrate]/[Fe(III)] <1/3 in HCl-citric acid medium inhibited the corrosion by possible polymerization of polyneuclear citrate-iron complexes and their sedimentation.