The QM9-G4MP2 database is built upon the existing QM9 data set by providing highly accurate G4MP2 (Gaussian-4 theory using reduced order perturbation ) calculations for the molecular structures within QM9. The G4MP2 approach employed in this database comprises the calculations with a series of methods including DFT, Hartree-Fock (HF), Møller-Plesset perturbation theory (MP2), and coupled-cluster single and double excitations with perturbative triple correction (CCSD(T)).