PURPOSE: To obtain polyvinyl alcohol deriv. useful for the preparation of resist for color filter having excellent dyeability, heat resistance, and stability by allowing aminoacetal to react with specified polyvinyl alcohol deriv. having introduced pyridinium group.

CONSTITUTION: Formyl styryl pyridinium salt expressed by the formula I (wherein R is methyl or ethyl; X is Cl, Br, I, etc.) is allowed to react with polyvinyl alcohol or partially saponified polyvinyl acetate in the presence of acidic catalyst. Then, obtd. polyvinyl alcohol deriv. having introduced styryl pridinium group expressed by the formula II (wherein n, n' are integers) is allowed to react with aminoacetal in the presence of acidic catalyst to obtain polyvinyl alcohol deriv. expressed by the formula III and having ≥75% degree of saponification (wherein R' is aminoalkyl; l, m, and n are integers). By using this polyvinyl alcohol deriv. as starting material, an aimed resist for color filter is obtd.