The effect of valinomycin on phospholipids (unidentified phospholipid (UI, possibly cardiolipin), phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (Sph), lysophosphatidylcholine (Lyso-PC) and total phospholipid in the isolated rat submaxillary glant was examined and following results were obtained. 1. In the presence of 1 μM, 10 μM and 100 μM valinomycin, no significant differences were observed in the content of UI, PE and total phospholipid, as compared with the experimental control. 2. In the presence of 1 μM, 10 μM and 100 μM valinomycin, the content of PC was increased, and that of Lyso-PC was decreased. 3. In 1 μM and 10 μM valinomycin, no significant changes were observed in the content of Sph, whereas in 100 μM valinomycin, the decreasing tendency was observed in the content. From the above mentioned results, it was suggested that these changes in the contents of PC, Lyso-PC and Sph might be due to the inhibition of phospholipase A activity and of the other enzymic activity, like that of phospholipase A and also the significance of the results obtained was discussed.