To provide a method for producing 1,3-dioxane, by which 1,3-dioxane is efficiently produced from ethylene and formaldehyde and a catalyst is readily recovered.

The method for producing 1,3-dioxane comprises reacting ethylene with formaldehyde in the presence of a partially neutralized heteropoly acid (B) obtained by exchanging a part of the proton of a heteropoly acid (A) with a lithium cation and/or a silver cation. The heteropoly acid is, for example, selected from the group consisting of heteropoly acids represented by general formula: H3PW(n)Mo(12-n)O40 and H4SiW(n)Mo(12-n)O40 (n is 0 or a positive integer of ≤12; H is a hydrogen atom; P is a phosphorus atom; Si is a silicon atom; Mo is a molybdenum atom; W is a tungsten atom; O is an oxygen atom).