The current study includes the dual effect of changes in temperature and pH on stability of cefquinome in vitro. Cefquinome was exposed to different phosphate buffer solution with a pH of 6,7 or 8 and each one was exposed to different temperatures which were 30̊C,50̊C or 70̊C in a water bath during 24 hours. Samples were collected after dissolving, after exposure to different pH and after 1,3,6,12 and 24 hours of exposure to different temperatures and pH values. Microbiological assay was used to analyze the samples. The results showed that there was a significant decrease in cefquinome concentrations (antibacterial activity) in alkaline medium with increasing temperature within the time. In conclusion cefquinome is affected by increasing temperature in alkali medium which causes a decrease in its concentration that will affect efficacy of cefquinome due to the degradation process.