In May 1995, Mossbauer Spectroscopies for cormsion substances formed on a low alloy(16Mn) steel, exposed in Chengclao sea area for 2 year from DeL 1992 to Cct 1994, were derived.The phase composihon and content of the rust layers on the 16Mn steel in four different mdrinccormsion zones (i. e. splash zone, hde zone, seawater zone and seamud zone) were analyzed andstUdied. In every corrosion zone, the rust layer of the 16Mn steel is maiuly composed of four kindsof chewhcal composihons including α－Fe3O4(A), α－Fe3O4(B), β－FeOOH and a－FeO. β－FeOOH is thedondnant composihon, which is a typical cormsion substance of steel in marine environinnts. Thedifferent contentS of β－FeooH and a－Fe3O4 in rust layers illustrate that β－FeOOH in the inner rustlayer is involved in the cathodic process as the oxidanL eccelerahng the cormsion of the low alloysteel under wet/ dry cycle conditions. on the other hand, for the alloy elements in the 16Mn steel,the rust layers with simple composition and fine and close textures form a good barrier layer,lowering the corrosion rate of steel and increasing the resistance of the 16Mn steel against marinecormsion.