Abstract: On the basis of structure-activity relationship of some antimalarial drugs, the authors synthesized a new compound 2-methoxy-7-chloro-10-3′, 5′-bis (pyrrolidinomethyl)-4′-hydroxyanilino benzob 1,5-naphthyridine(Ⅰ), coded 7351 and named poyronaridine. The compound exhibited high schizonticidal activity and low toxicity. Since then, a seriesof analogues Ⅱ, 2-substituent-7-chloro-10-3′,5′-bis-or 3′-mono-(substituted aminomethyl)-4′-or 2′-hydroxyanilino benzob-1,5-naphthyridines (Table 4), were synthesized.Compound Ⅰ and its analogues Ⅱ were prepared with 2-substituent-5-aminopyridines as intermediates. These intermediates were. condensed with 2,4-dichlorobenzoic acid to give 2-substituent-5-(2-carboxy-5-chloroanilino) pyridines (Table 1) which were cyclized in the presence of phosphorus oxychloride. The cyclized products 2-substituent-7,10-dichlorobenzob 1,5-naphthyridihes (Table 2) were subsequently condensed with 4-or 2-hydroxyaniline to form 2-substituent-7-chloro-10(4′- or 2′-hydroxyanilino)benzob1,5-naphthyridines (Table 3), the latter being finally, reacted with Mannich reagents to yield the desired compound Ⅰ and its analogues Ⅱ.Among the analogues Ⅱ, most compounds were effective in varying degress against the murine blood schizonticidal test, and the analogues Ⅱ_{1～6, 9, 10} were as effective as compound Ⅰ. In addtion, compounds Ⅰ and Ⅱ_{1, 3, 5, 6, 9, 10, 12, 15} were also highly effective against Plasmodium yoelii-Anopheles stephensi-mouse system, their potency being superior to that of primaquine. It was noteworthy that the substituted benzo-b1,5-naphthyridines were effective, not only against P. berghei of blood transmission, but also against P. yoelii through the sporozoite inoculation.