Objective To explore the characteristic impairments of olfactory working memory in the transgenic mice at very early stage of Alzheimer’s disease (AD). Methods Nine pairs of 5?week?old male 5XFAD mice and their wild?type littermates, and 8 pairs of 9?week?old male 5XFAD mice and their wild?type littermates were used. The study animals underwent the odor span test after extensive training. The odor span length, the number of errors and the accuracy rate of odor discrimination were used to evaluate the olfactory working memory. Results Compared with the wild?type group, the 9?week?old transgenic mice presented significantly shorter odor span length ( P < 0. 05), more errors ( P <0. 05) and lower accuracy ( P < 0. 05) of odor discrimination. Besides, the 9?week?old transgenic mice exhibited significantly shorter odor span length than the 5?week?old transgenic mice ( P < 0. 05). However, there were no significant differences in the odor span length, the number of errors and the accuracy between the 5?week?old transgenic and wild?type mice ( P > 0. 05). Conclusions Olfactory working memory is impaired in the 9?week?old transgenic 5XFAD mice. It suggests that the olfactory working memory impairment might be considered as a sensitive indicator of very early cognitive impairment in the 5XFAD mice.