In this work, we found that the open-metal site in a metal-organic framework (MOF) can be used to enhance such selectivity. Hydrogenation of phenyl acetylene over such a catalyst enables ultrahigh styrene selectivity of 92% at full conversion with a turnover frequency of 98.1 h(-1). The origin of ultrahigh selectivity, as unveiled by density functional theory calculation, is due to a coordination interaction between the open Zn(II) site and the C C bond of phenylacetylene.