Abstract: 1. Out of forty-seven kinds of drugs experimentally tested in mice infected with Japanese B encephalitis virus, 9 were shown to possess certain therapeutic effects; they are phenelzine, funacillin, 8-azaguanine, thiosemicarbazide, propadrine, deoxyephedrine, phenylhydrazine, isonicotinylhydrazide, 6-MP. 2. Of particular interest was the observation that phenelzine and funacillin inhibited the multiplication of Japanese B encephalitis virus in mouse brain. 3. By analysing the relationship between chemical structures and therapeutic actions of such effective substances as hydrazine benzyl compounds, cyclo semicarbazide, ephedrine analogues, anti-purine compounds, it is reasonablly expected that those compounds may be used as tools for further studies to throw additional light on the chemotherapeutic mechanism of action against Japanese B encephalitis virus.