Peroxynitrite　is　a　potent　oxidant　in　vivo　which　can　result　in　serious　diseases　such　as　cardiopathy,　acute　inflammation　and　even　cancer.　Iron　porphyrins　have　been　shown　to　catalyze　the　efficient　decomposition　of　peroxynitrite　and　are　therefore　important　to　detoxify　the　cytotoxic　oxidant　as　therapeutic　agents.　A　kinetic　and　theoretical　study　on　peroxynitrite　decomposition　catalyzed　by　iron　porphyrins　is　carried　on　in　order　to　search　and　synthesize　more　effective　scavengers　of　peroxynitrite.　Kinetic　experiments　and　quantum　chemistry　calculations　were　applied　to　iron　porphyrins　with　different　substituents　for　catalyzing　peroxynitrite　decay.　Kinetic　experiments　suggested　that　the　catalytic　ability　of　iron　porphyrins　for　peroxynitrite　decomposition　were　dependent　on　the　type　and　location　of　substituents　on　the　porphyrin　rings.　Density　functional　calculations　further　reveal　that　the　variation　of　substituent　leads　to　a　difference　in　structure-related　quantum　chemical　descriptors　including　charges　of　central　metal　ion,　energy　of　the　highest　occupied　molecular　orbital　and　energy　of　the　lowest　unoccupied　molecular　orbital.