Abstract: This paper reports the result of study on the formation of monoalkyl long chain acidic phosphate in the 30% TBP-n-dodecane-HNO3 under strong irradiation condition. The result shows that the TBP content plays a very important role on the formation of monoalkyl phosphate, whereas DBP, MBP do not. Under irradiated condition of absorbed dose of 5×106Gy, the concentration of monoalkyl long chain acidic phosphate is as high as 8. 4×10-3mol/l. The mechanism of formation of monoalkyl long chain acidic phosphate is discussed.