Proteinase inhibitors are widely distributed in the plant kingdom and associated with the resistance of plant against insects and pathogens. Ingestion of some plant proteinase inhibitors in the artificial diet can retard the growth and development of insects, even cause the insects dead. Transgenic plants of proteinase inhibitors derived from plants definitely show effects of insect-resistance. Insects can reduce the growth and development inhibition by secreting gut proteinases that insensitive to plant proteinase inhibitors existed in the diet. The quantity and quality of food proteins are very important in dictating the anti-nutritional effects of plant proteinase inhibitors on insects. Plant proteinase inhibitors can be induced by the infection of many plant pathogens, and the growth of microorganism isolated from the spoiled tissues can be inhibited by the induced plant proteinase inhibitors. Progress in the roles of plant proteinase inhibitors in the resistant mechanism of plant against insects and pathogens was reviewed.