Erythromycin and Roxithromycin both belong to macrolide antibiotics, both have similarity in antibacterial spectrum, but there are some differences in the effect on different strains of bacteria and side effects. Roxithromycin belongs to the new generation of drugs compared with erythromycin, which is a semi-synthetic antibiotic. Both can be used in the treatment of mycoplasma, chlamydia and other infections, but as a new generation of drugs, the effect of erythromycin is better than erythromycin, and erythromycin can also inhibit gram-positive bacteria and syphilis spirochetes. In terms of side effects, erythromycin may cause gastrointestinal symptoms such as diarrhea, nausea, vomiting, etc.; erythromycin also has a certain degree of hepatotoxicity, which may damage the liver; roxithromycin side effects are much milder. Patients are advised to apply both drugs rationally under the guidance of physicians.