Abstract: In order to study the sensitivity of the Neochloris oleoabundans to cloramphenicol,penicillin,streptomycin and tetracycline,the growth of algal cells was observed in the media with the antibiotics at the concentrations of10,25,100 and 500 μg / m L under liqid culture and agar medium plates.The results revealed that all these four kinds of antibiotics could inhibit the growth of alga cells.Among the four antibiotics,streptomycin had a severe inhibition to the alga growth as the completely inhibiting concentration was 10 μg / m L,while the inhibition concentrations of chloramphenicol and tetracycline were 100 μg / m L. However,penicillin behaved inhibition only when the concentration of it reached to 500 μg / m L. The data analysis showed that the half inhibitory concentrations of streptomycin,tetracycline,cloramphenicol and penicillin were 0.25,72,119 and 164 μg / m L respectively.Under solid culture,the inhibition concentrations of streptomycin,chloramphenicol and tetracycline were 10,100 and 100 μg / m L respectively,while penicillin behaved no significant inhibition effection on the alga growth.