Efficient dehydrogenation of cyclohexane at low temperatures is of great importance in the field of liquid organic hydrogen carriers (LOHCs). In this paper, a series of Pt nanoparticles with a size distribution of 1.6-3.1 nm were loaded on nitrogen-doped carbon (Pt/CN) as the catalysts for cyclohexane dehydrogenation under low temperatures (180-210 degrees C). The effect of the Pt particle size on its catalytic performance was systematically explored. It is found that a volcanic trend exists between Pt particle size and its catalytic activity for cyclohexane dehydrogenation. The conversion of cyclohexane to benzene reaches up to 96.03% at 210 degrees C within 90 min using the Pt/CN catalyst with a Pt particle size of 1.9 nm. The corresponding activation energy of cyclohexane dehydrogenation is calculated to be as low as 36.2 kJ.mol(-1) when compared with that using the other synthetic catalysts. By detailed characterizations of all Pt/CN catalysts, it is deduced that the Pt particle size effect on cyclohexane dehydrogenation can be attributed to the competition between the increased active sites and the covered active sites by products when decreasing the Pt particle size. This work provides not only a systematic study on the size effect of Pt particles but also a new way to design efficient and stable catalysts for cyclohexane dehydrogenation.