Cyclophosphamide is an antineoplastic agent that also has immunosuppressive properties. Adverse reactions can be manifested in several ways, firstly, on the hematological system, which can lead to bone marrow suppression, of which leukopenia occurs more commonly, usually at a minimum value of 1-2 weeks after administration, and most patients can recover in 2-3 weeks after symptomatic treatment. In addition, cyclophosphamide may also have an effect on liver function, and some patients may develop abnormal liver function after using cyclophosphamide. Because it is also a chemotherapeutic agent, there may also be gastrointestinal reactions associated with chemotherapy drugs, including loss of appetite, nausea, vomiting, and other gastrointestinal adverse reactions, which usually recover 1-3 days after stopping the drug. There are also urological reactions. When high doses of cyclophosphamide are used, or when cyclophosphamide is administered intravenously by drip, there is a risk of hemorrhagic cystitis, which can manifest as urinary tract irritation, such as oliguria, hematuria, and proteinuria, etc. This is caused by the irritation of the bladder by the metabolites of cyclophosphamide. However, the probability of bleeding cystitis due to cyclophosphamide at regular doses is usually low. Other reactions include hair loss and stomatitis due to cyclophosphamide, as well as skin pigmentation and menstrual disorders. In addition, cyclophosphamide may also cause toxicity in the male reproductive system, which may result in azoospermia or sperm reduction. In conclusion, cyclophosphamide is an antineoplastic drug and some of its adverse reactions may be similar to those of antineoplastic drugs. We must closely monitor the adverse reactions of cyclophosphamide during its use.