Five imidazolium-type ionic liquids, containing both N1-unsatured chain and N3-long alkyl saturated chain as cations and hexafluorophosphate as anion (VImC(x)PF(6), x=4, 8, 12, 18 and 22), were evaluated as corrosion inhibitors for carbon steel SAE 1018 in 1.0 M H2SO4 solution. The compounds presented relatively high inhibition efficiencies (similar to 81-96%) at 100 ppm as confirmed by weight loss tests and polarization curves. Synthesized inhibitors obeyed Langmuir adsorption and behaved as mixed type inhibitors, displaying physical and chemical adsorption depending on the length of the carbon chain link to N3. Mossbauer analysis of corrosion products mainly determined the presence szomolnokite (FeSO4 H2O), whose content increased with aliphatic chain length suggesting that corrosion inhibition occurred by iron sulfate formation. The most effective compound (VImC(12)PF(6)) was the only that displayed the presence of alpha iron, iron hydroxide and rozenite (FeSO4 4H(2)O) as corrosion products.