OBJECTIVE： To investigate the stability of Vidarabine monophosphate for injection combined with Aciclovir injection. METHODS： HPLC method was adopted. The content variations of two drugs in mixture were determined within 8 h at 5 ℃，25 ℃，35 ℃ under dark and light. The changes in appearance， property， pH value and insoluble particles （within 24 h） were investigated before and after compatibility. RESULTS： There were no significant changes in appearance and pH value at 5 ℃，25 ℃，35 ℃ under dark， and insoluble particles were in line with Chinese Pharmacopoeia（2010 edition），and the relative content of vidarabine monophosphate and aciclovir were above 99％ （compared with 0 h） within 8 h. Under the light conditions， as the temperature raised and the extension of storage time， the content of vidarabine monophosphate did not significantly decrease， but that of aciclovir had declined significantly（4 h and after 4 h）， while pH value also had a certain degree of rise； the insoluble particles had no obvious change. CONCLUSIONS： The mixture of vidarabine monophosphate and aciclovir in 0.9％ Sodium chloride injections is stable under dark conditions within 8 h； it is suggested that the mixture should be used up within 4 h after mixing and protect from light to guarantee the safety of drug use in the clinic.