The site of the synthesis of Japanese encephalitis virus(JEV) in the actinomycin-treated and infecter PS Y15 cells(a porcine kidney stable cell line) was observed by the immunofluorescent antibody technique, acridine orange staining, and the autoradiographic analysis. In the parallel studies by immunofluorescent technique and acridine orange staining it the infected cells, Viral protein(as an antigen) and viral RNA were detected at the same site of cytoplasm. In the autoradiographic analysis, the cytoplasmic labeling of $^3H$-uridine was due to the synthesis of JEV-RNA, while the nucleolus and nucleus were not involved. In the autoradiographic studies on the secton of infected cells, the $^3H$-uridine was frequently incorporated around the cytoplasmic vacuoles. This localization of labeling agreed with the site of acridine orange positive granules. The results suggest that the syntheses of the viral RNA and viral protein occurred in the similar site of cytoplasm of the infected cells, and also the virus particles seem to be assembled in the sites of the viral RNA and protein syntheses.