A new ionic liquid, N-octyl-2-pyrrolidonium chloride (NOPC), were synthesized and evaluated as inhibitors for mild steel (Q235) corrosion in 1 mol/L HCl. The adsorption behavior and corrosion inhibition mechanism of NOPC for mild steel in HCl solution were investigated by using weight loss measurements, electrochemical techniques, and SEM. The inhibition efficiency increases with the increasing concentration of NOPC in 1 mol/L HCl and decreases as the temperature increases. The results indicate that NOPC is able to function as a mixed type inhibitor.