The study was undertaken to assess the CT density of the antibiotics solution. CT scan of six antibioticssolution-streptomycin, chloramphenicol, Na-penicillin, ampicillin, kanamycin and cefamezine-in concentration ofabout 33% (approximatly single dose of intramuscular injection) was performed, using plastic syringes. Variousconcentrations of striptomycin, chloramphenicol and Na-panicillin were also examined for evaluation of relationbetween concentration and the CT density of the antibiotics. In addition, relationship between CT number andmathematically calculated effective atomic number and electron density of the antibiotics was evaluated. Theresults are as follows; 1. The CT densities of all antibiotics reveal high density (CT number 80–150) inconcentration of single intramuscular injection dose. 2. CT number of striptomycin, chloramphenicol andNa-penicillin gradually increased with increase of concentration of the antibiotics, producing linear proportionto concentration, effective atomic number and electron density of the antibiotics. 3. Therefore, density ofantibiotics should be included in differential diagnosis when high density on CT scan is observed.