Polysaccharide aldehydes having the formula Sacch--O--CH.sub.2 --CH.dbd.CH--CHO, ##STR1## such as starch, cellulose, and gum aldehydes, are useful for imparting wet, dry, or temporary wet strength to paper. They are prepared by a non-oxidative method which involves reacting the polysaccharide base, in the presence of alkali, with a derivatizing acetal reagent having the general structure ##STR2## and then hydrolyzing the acetal by adjusting the pH to less than 7, preferably 2-4. In the formulas, n is 1-3; R.sup.11 and R.sup.12 are independently an alkyl, aryl, aralkyl, or alkaryl group when n is 1, R.sup.11 or R.sup.12 is one of the groups when n is 2, or R.sup.11 and R.sup.12 are not present when n is 3; R.sup.13 is an alkyl group, optionally containing an ether linkage, or an aralkyl group; R.sup.14 and R.sup.15 are individually a hydrogen or a methyl group; R.sup.16, R.sup.17, and R.sup.18 are individually an alkyl group; Y- is an anion; Z is an organic group capable of reacting with the polysaccharide base to form an ether derivative and selected from the group consisting of an epoxide, ethylenically unsaturated group, halohydrin, and halogen; R.sup.19, if present, is a divalent organic group containing no reactive substituents; and A and A'0 are lower alkyls or together form at least a 5-membered cyclic acetal.