The inhabitant activities of shaddock peel extracts (SPE) against bacteria, yeasts and molds were studied. the rcsults showed that SPE had strong inhabitant activities against Bacillus thurrngiensis,Staphylococcus aureas and bacteria from pickle, but weak against Escherichia coli, Salmenella entenitidis,Aspergillus niger and no inhabitant effects against Saccharomyces cerevisiae, Rhodo torula, Penicillium glaueus. The variation of pH did not significantly affect the functions of SPE on microorganisms.