HIV protease has been proved to be one of the most effective targets for finding anti-HIV agents. Some inhibitors of this enzyme have been developed as potent anti-AIDS drugs. However, new anti-HIV chemotypes of low toxicity and of potentially low cost are still needed. This review includes recent researches on HIV protease inhibitors isolated from plant sources and their structural modification. Some triterpenes (e.g. ursolic acid and oleanolic acid), polyamides (e.g. tricoumaroylspermidine), saponins (e.g. escin Ia), lignans (e.g. longipedunin A) and other compounds were found to have moderately to potently inhibitory activity against HIV-1 protease. Structural modification of some of the natural compounds or synthesis of their analogs led to more potent HIV protease inhibitors. Some triterpene derivatives inhibited HIV protease based on the mechanism of dimerization inhibition, which is different from the mechanism of the clinically used HIV protease inhibitors.