Boryl- and amino-substituted acetylenes would have a butatriene-type resonance contribution due to the interaction between boron empty orbital and nitrogen lone pair. However, a few examples of boryl- and amino-substituted acetylenes have been synthesized up to date, and structural analysis by X-ray crystallography has remained unknown. Here we report the synthesis and characterization of dimesitylboryl- and diethylamino-substituted acetylene. In addition to the spectroscopic studies, the X-ray crystallography of the acetylene revealed the lengthening of the triple bond and the shortening of C-B and C-N bonds, being consistent with the butatriene-type resonance contribution.