Metal nanoparticles (MNPs) have potential uses in biochemical sensing applications owing to their localised surface plasmon resonance (LSPR) characteristics. In practice, selective biochemical sensors based on LSPR are constructed by MNPs and selective receptors for specific biochemical molecules. This Letter studies the effects of receptor thickness on LSPR sensing properties experimentally and theoretically. Experimental results demonstrate that an increase in polymethyl methacrylate (PMMA) receptor thickness induces a red shift of LSPR spectrum. For a 42 nm PMMA receptor, the maximum extinction efficiency is more sensitive to the test chloroform vapour than the peak wavelength. This receptor thickness effect is confirmed by electrodynamics calculations: a relatively thin receptor layer will create high peak wavelength sensitivity and low extinction efficiency sensitivity. However, it is the opposite for a relatively thick receptor layer. The turning point between thick and thin is approximately 20 nm in this Letter. These insights can be used as guidelines in fabricating high-sensitive LSPR-based biochemical sensors.