This paper describes in detail the metal-loaded liquid scintillator (LS) that was developed for use in reactor neutrino experiments. Two different organic base solvents, linear alkyl benzene (LAB) and diisopropylnaphthalene (DIN), are used to synthesize the liquid scintillator. Gadolinium (Gd) or lithium ( 6 Li) is loaded into the organic liquid scintillators. A solvent-solvent extraction method was developed to load Gd into LS, and in the case of 6 Li, a suitable surfactant was found and was applied. In this study, the optical and the physical properties of the LS were investigated, and the results summarized in this report, including the transmittance, emission spectra, light yield, pulse shape discrimination, and water concentration.