BN-supported Pt catalysts were prepared by an impregnation method using Pt(NH3)(4)(NO3)(2) as metal precursors and tested in the liquid-phase selective hydrogenation of cinnamaldehyde. It was found that the Pt/BN catalyst exhibited a high performance for the selective C=O hydrogenation at room temperature. A selectivity of over 85% towards cinnamyl alcohol at a cinnamaldehyde conversion of over 95% could be obtained. The effects of supports and Pt particle sizes were explored by N-2 physisorption, XRD, TEM, HRTEM, HAADF-STEM, TPD, H-2-TPR, XPS, CO-DRIFTS, etc. The influences of solvents and operation conditions were investigated, and a simplified kinetics test was also carried out. The comparison of different supports suggested that BN with an inert surface and few acid-base sites possibly favors a simple adsorption mode of cinnamaldehyde dependent only on the supported Pt particles, resulting in a high selectivity to cinnamyl alcohol. While the abundant acid-base surface sites on the Pt/Al2O3 or Pt/SiO2, possibly associated with the multiple adsorption modes of cinnamaldehyde, had an adverse effect on the selective C=O hydrogenation. The investigation of Pt size effect showed that large Pt particles with few low coordinated Pt sites displayed a higher selectivity to cinnamyl alcohol than small Pt particles with more low coordinated Pt sites on the Pt/BN catalysts. It was also revealed that water is a suitable solvent, and the presence of water in a mixture solvent is crucial for achieving a high activity of the Pt/BN in cinnamaldehyde hydrogenation.