Additives play a pivotal role in achieving high-quality electrodeposited cobalt films for diverse applications in microelectronics. In this work, 1,4-butynediol (BYD) bearing function groups of CC and -OH, 1,4-butenediol (BED) featuring C = C and -OH, and glycol (EG) with only -OH were studied to reveal the potential underlying mechanism of unsaturated carbon bonds on cobalt electrodeposition. It is found that BYD inhibits both the cobalt deposition and the formation of adsorbed hydrogen, forming compact cobalt film. Furthermore, the surface and cross-section morphology, grain structure, and resistivity of electrodeposited cobalt are characterized to investigate the effects of alkynol additives. It was observed that BYD induces a change in surface morphology from a mixture of elongated ridges and granular shapes to a flattened granular structure. The texture of the electrodeposited cobalt film transformed from hcp(100) and hcp(101) to hcp(002) with the addition of BYD due to the selective absorption of BYD on specific cobalt orientation. This study not only regulates the grains orientations and properties of electrodeposited cobalt, but also enhances the comprehension of the effect and mechanism of unsaturated carbon bonds on cobalt electrodeposition. These findings provide a theoretical foundation for the selection of additives and their practical applications.