Chloramphenicol (CAP) is a very effective broad-spectrum antibiotic which had been widely used in animal production. However, the drug is not approved in many countries for use in food-producing animals because of its potential toxicity and the possibility of residues in food products. In this study, a modified microbiological assay was developed for the sensitive detection of CAP residues in meat and milk. The method was characterized by the extraction of CAP with ethyl acetate, addition of $0.15;mu extrm{g}$ oxytetracycline/ml in the phosphate buffer diluent (pH 6.0), a luteus ATCC 9341. The lowest levels of CAP detected in muscle tissues and milk were $0.025;mu extrm{g}/ml;and;0.05;mu extrm{g}/g$, respectively. Recovery rates free CAP from milk were 68.5%, from bovine muscle 65.1%, from swine muscle 63.8%, and from chicken muscle 59.4%, respectively, and the coefficients of variation were 1.8~15.1%. The results showed that the detection limits of CAP residues in animal products could significantly be improved by the modified microbiological assay than the conventional ones.