Abstract: To study the activities of bio-preservatives 2-phenylethanol(2-PE),natamycin,chitosan and oligochitosan against the four mainly citrus pathogens Penicillium italicum,Penicillium digitaum,Alternaria citri and Cladosporium cladosporioides,the antibacterial rate and minimum inhibition concentrations of sigle and composite biopreservatives were assayed in this research. The results showed that both of 2-PE and natamycin strongly inhibited the four pathogens in therelative low mass concentration,and could inhibite mycelium growth of citrus pathogens in the concentration of 2.4 g/L(2-PE)and 0.3 g/L(natamycin). The antibacterial effects of chitosan and oligochitosan were not significant,and mycelium growth could not be inhibited completely in relative high concentration of 7.5 g/L(chitosan)and 12.0 g/L(oligochitosan). The analysis of variance of main effect and interaction effect showed that the main factors affecting the inhibition rate of Penicillium italicum and Cladosporium cladosporioides were 2-PE and natamycin,and the interaction between 2-PE and natamycin was significant(0.005 < P < 0.05). The interaction between 2-PE and chitosan was not significant(P>0.05). Combined usage of 2-PE and natamycin could enhance their inhibition activities significantly(P<0.05). Compared with the same concentration of 2-PE,the antibacterial effect would increased by more than 60% when 2-PE and natamycin were combined.