Studies on humans and rodents indicate possible long-term cognitive impairment after surgery or general anesthesia. The goal of this study was to evaluate the effect of various anesthetic concentrations on spatial learning in adult mice. The behavior of adult mice in a T-maze was assessed 28 h after anesthesia (control [0%], low [1%], or high [2%] isoflurane concentration). The mice anesthetized with 1% isoflurane had a significantly poorer performance than did the other 2 groups. The performance of the mice anesthetized with 2% isoflurane was not statistically different from that of the control group. Therefore, low, not high, isoflurane concentration impaired spatial learning in mice.