A series ofnd δ1Δg Rydberg states of the Li2 molecule has been measured using the polarization labelling technique. The experimental term values and the quantum defects derived from them, are compared with theoretical values obtained from ab initio calculations. The different physical effects contributing to the quantum defects are discussed. It turns out that perturbations of the Rydberg states by the doubly excited configurations with the atomic asymptotes 2p+2p have a significant influence on the quantum defects.