provided are novel superoxide dismutase derivatives represented by the following general formula ## str1 ## wherein is a superoxide dismutase residue derived by removal of two mercapto groups , and w is a divalent long chain hydrocarbon residue which may optionally be interrupted by one or more groups each independently selected from the group consisting of an oxygen atom , a sulfur atom and a group of -- n -- . the sod derivatives retain most of the enzymatic activities of unmodified sod and have much longer plasma half - life than unmodified sod . they are effective for treating various diseases caused by active oxygen species . also provided are chemical modifiers to prepare the above sod derivatives .