PURPOSE: To readily obtain myoinositol polyphosphate having the possibility as a medicine by reacting myoinositol with an acyl halide, providing a polyacylmyoinositol and then reacting the resultant compound with a phosphorylating agent.

CONSTITUTION: Myoinositol is reacted with an acyl halide (preferably benzoyl chloride) to provide a 1,3,5-triacyl derivative and a 1,3,4,5-tetraacyl derivative. A substituent group R is then introduced into the 4-position of the triacyl derivative and protecting groups are introduced into the 2,6-positions of the triacyl derivative and the tetraacyl derivative. The acyl groups and substituent groups are subsequently eliminated and the resultant derivatives are reacted with a phosphorylating agent of 1,5-dihydro-3-dialkylamino-2,4,3-benzodioxaphosphepins expressed by the formula (R is lower alkyl; R1 is H or lower alkyl; R2 is H or methoxy) and then catalytically reduced to provide myoinositol 1,3,5- triphosphate.