The invention relates to a method for producing NCO-modified polyoxymethylene block copolymers comprising the step of polymerizing formaldehyde in a reaction vessel in the presence of a catalyst, the polymerization of formaldehyde in addition taking place in the presence of a starter compound comprising at least 2 Zerewitinoff active H atoms to obtain an intermediate product. The intermediate product obtained is reacted further with an isocyanate to obtain an NCO-modified polyoxymethylene block copolymer. The invention also relates to NCO-modified polyoxymethylene block copolymers obtained by a method of this type and to the use of said copolymers for producing polyurethane polymers.