The adsorption of cyclohexene (C6H10) on Pt(111) and two ordered PtnSn/Pt(111) surface alloys has been investigated experimentally using high-resolution electron energy loss spectroscopy (HREELS), low-energy electron diffraction (LEED), and temperature programmed desorption (TPD) as well as theoretically by ab initio density functional theory (DFT) calculations. On Pt(111) and Pt3Sn/Pt(111) a di-σ-bonding of cyclohexene has been found both experimentally and in the DFT calculations. In contrast, on the Pt2Sn/Pt(111) a mixture of weakly bound species (di-σ, π, and physisorbed) has been found. Whereas on Pt(111) a considerable fraction of the cyclohexene dehydrogenates during thermal treatment, the adsorption is completely reversible on the two surface alloys. A detailed theoretical study of the structure and vibrational spectra of the dehydrogenated species has been performed on Pt(111). This allowed the interpretation of the variations in the HREELS spectra when the flash temperature increases by the formation of some dehydrogenated products.