An efficient procedure has been proposed for the synthesis of linear and angular phenyl-substituted dibenzonaphthyridines from anilinoquinolines and benzoic acid in up to 85% yield using Eaton’s reagent (a solution of phosphorous pentoxide in methanesulfonic acid) as condensing agent instead of polyphosphoric acid which previously afforded less than 50% yield of the same compounds. Apart from benzoic acid, ethyl benzoate and benzoyl chloride can be used in the synthesis of dibenzonaphthyridines according to the proposed procedure, but the yields are lower.