Macrophages play a critical role in mediating inflammatory processes; activated macrophages respond to endotoxin by releasing pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6. Ketamine, a widely used anesthetic agent, has unequivocally anti-inflammatory effects in vivo and in vitro. However, the detailed mechanisms for the anti-inflammatory effects of ketamine in microglia have not been elucidated yet. This study aimed to evaluate the effects of ketamine on lipopolysaccharide (LPS)-induced nitric oxide (NO), hydroxyl radical (·OH) production, and intracellular calcium accumulation in macrophages. Macrophages were pretreated with ketamine at the concentrations of 10, 100, and 1,000 μM 1 h before LPS stimulation. The production of NO and ·OH in the culture supernatant of macrophages was assayed by Griess Reagent Kit. LPS enhanced NO and ·OH production and provoked a significant intracellular calcium elevation. With the concentrations higher than 100 μM, ketamine inhibited LPS-induced NO and ·OH accumulation and intracellular calcium elevation. However, a low concentration of ketamine (10 μM) did not exert anti-inflammatory effects. These results suggest that intracellular calcium elevation is, at least, partially involved in the inhibitory effect of ketamine.