Effects of Mo and Mn elements on pitting corrosion resistance of lean duplex stainless steel in C1- media solution have been studied. Gravimetric tests in 6 mass% FeCl3 at 35 ℃ and potentiodynamic analysis in 3.5 mass% NaCI were carried out. The corrosion potential （Ecoor） and the pitting potential （Epit） are shifted to a more noble po tential because of the presence of Mo around the pits. While the presence of Mn could sharply reduce the value of pitting resistance equivalent number （PREn） and the pits can be formed more easily. The pits are found generating at the phase with a lower PREn. The identical tendencies between the Epit and PREn of weaker phase are the same. A corrosion mechanism has been proposed to determinate pitting corrosion behavior based on microstructural observations.