Chlamydia is a kind of organism smaller than bacteria but larger than virus, which has two stages of life cycle. Namely infectious protozoa (EB) and non-infectious protozoa (RB). EB particles are spherical, small and dense, with a diameter of 0.2? 0.4μm, barely visible under ordinary optical microscope; EB is a mature chlamydia, which mainly exists outside the cell. RB is an immature stage of chlamydia in the development cycle of host cells, which is reproductive and non-infectious. Chlamydia is an obligate intracellular parasitic pathogen similar to bacteria and viruses, belonging to Chlamydia, Chlamydia (only one family) and Chlamydia, with four species (namely, Chlamydia pecorum, Chlamydia psittaci, Chlamydia Trachomatis and Chlamydia Pneumoniae). Its characteristics are as follows: ① there are two kinds of nucleic acids, deoxyribonucleic acid and RNA, which proliferate in binary division mode and have ribosomes and membranes similar to cell walls; ② Intracellular parasitism, totally dependent on the energy supply of the host cell (due to lack of ATPase); ③ Its life cycle can be divided into two stages: extracellular stage (infectious body) and intracellular stage (proliferative reticular body). ④ Chlamydia inclusion bodies can be found in protoplasm near the nucleus by Giemsa or fluorescent antibody staining; ⑤ The genome Mr of chlamydia is 660× 106, which is smaller than any prokaryote except mycoplasma. There are three kinds of chlamydia that cause human diseases: Chlamydia psittaci, Chlamydia trachomatis and Chlamydia pneumoniae discovered in recent years; ⑥ In addition to smear test, complement fixation test and micro-immunofluorescence test, chlamydia can be isolated directly by cell culture. ⑦ Tetracyclines and erythromycin have good therapeutic effects, and quinolones and other antibacterial drugs also have certain curative effects.