An octahedral metal-organic framework (MOF), UiO-68, with two hydroxymethyl groups (UiO68-hyd) was synthesized for the first time and the hydroxy groups were post-synthetically modified with iso(thio)cyanates to form (thio)urethanes. Several organotins and tertiary amines were used as catalysts for the modification of UiO68-hyd with butyl isocyanate (BuNCO), and 70% of hydroxy groups reacted after 7 days. Moreover, various isocyanate and isothiocyanate compounds were successfully modified on UiO68-hyd.