Objective To study the effect of substance P ( SP) on int racellular f ree calcium concent ration in human poorly-differentiated gast ric cancer cell in vitro. Methods Human gast ric cancer cell line MKN45 was cultured in RPMI 1640. Then the cells were loaded with specific calcium fluorescent probe Furu23/ AM. ASN21377642 (NK21 receptor antagonist) , Nicardipine (calcium channel blocker) and different concent rations of SP were used to treat gast ric cancer cells. The concent ration changes of int racellular free calcium were detected by laser scanning confocal microscope. Results It was found that 10 , 50 and 100 nmol/ L SP could significantly increase the int racellular free calcium concent ration of gast ric cancer cells in Hanks solutions , which contain ext racellular calcium ( P lt;0. 05) , and the change was in a dose-dependent manner ( P lt; 0. 05) . When there was ext racellular calcium existed ,the increasing amplitude of intracellular f ree calcium concent ration was significantly higher than that when there was no extracellular calcium ( Plt; 0. 05) . And when Hanks solutions were pretreated with ASN21377642 and Nicardipine , the effects of 100 nmol/ L SP were partly inhibited , and the concent rations of int racellular f ree calcium were significantly lower than those in group s without pret reatment s ( P lt; 0. 05) . Conclusion SP can significantly increase free calcium concent ration in the gastric cancer cells. Releasing of stored calcium in the cells and influx of extracelluar calcium may contribute to the elevation of int racellular free calcium concentration.