The extraction equilibrium of Mn(II) was clarified in novel synergic extraction systems using 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta) and neutral multidentate ligands, such as 2,2′ : 6′,2″-terpyridine (terpy) and tetraphenyldiphosphane dioxide (tpdpo), into benzene. No oxidation of Mn(II) and large synergic effect were observed both in the Htta–terpy and Htta–tpdpo systems, and quantitative extraction of Mn(II) was done, which was not attained with Htta only. Mn(II) was extracted as Mn(tta)2(terpy) in the Htta–terpy system, where only two nitrogen atoms of terpy would coordinate to Mn. In the Htta–tpdpo system, two species, i.e. Mn(tta)2(tpdpo) and Mn(tta)2(tpdpo)2, formed in the benzene phase, where tpdpo functioned as a unidentate ligand. The adduct formation constants (βs) and the synergic extraction constants (Kex,s) were obtained and compared with those of other related compounds.