Bimolecular rate constants for the gas-phase reactions of C_{2}(*X*^{1}*Σ*_{g}^{+}) with unsaturated hydrocarbons C_{2}H_{4} and C_{2}H_{2} were measured over the temperature range 293-573 K by pulsed laser photolysis/laserinduced fluorescence (PLP-LIF). The rate constants, in the unit of cm^{3}·molecule^{-1}·s^{-1}, can be fitted by the normal Arrhenius expressions: *k*(C_{2}H_{4})=(1.16±0.10)×10^{-10}exp[(290.68±9.72)/*T*], and *k*(C_{2}H_{2})=(1.36±0.02)×10^{-10}exp[(263.85 ± 7.60)/*T*], where all error estimates are ± 2σ and represent the precision of the fit. The observed bimolecular rate constants along with the negative temperature dependences of *k*(*T*) allow us to conclude that the reactions of C_{2}(*X*^{1}*Σ*_{g}^{+}) with these unsaturated hydrocarbons in the temperature range 293- 573 K proceed via an addition mechanism.