The sensing characteristics of molecularly imprinted polymer (MIP) coated Au nanoparticle (AuNP) sensors were adopted to detect α-pinene vapor. MIP was prepared by using methacrylic acid (MAA) as monomer, ethylene glycol dimethylacrylate (EGDMA) as cross-linker, and α-pinene as template. The MIP adsorption character was evaluated using GC-MS. The result demonstrated that the vapor adsorption amount of MIP is two times larger than that of non-imprinted polymer (NIP). The pre-polymerized MIP mixture was coated on ion-sputtered AuNPs substrate to fabricate the MIP-coated AuNP sensor. The influence of polymer thickness on the UV-vis spectra and the refractive index sensitivity (RIS) of MIP coated AuNP sensor were investigated. The coating of MIP resulted in a red shift of the Plasmon absorbance peak. The RIS of MIP coated AuNP sensor was higher than that of NIP coated one when the polymer thickness was controlled in the sensitive range of AuNPs. LSPR response of polymer-coated AuNP sensors exposure to α-pinene vapor was verified to be rapid, reversible, and reproducible.