Various kinds of 5, 6-dialkyl-2-thiouracils, 5, 6-dialkyluracils, and 3, 5, 6-trialkyluracils (alkyl : CH3, C2H5, C3H7, C4H9, iso-C4H9, C5H11, iso-C5H11), which were analogous with barbital in their chemical structures, were synthesized systematically, and relationship between pharmacological action and chemical structure was investigated. The compounds of this series showed sedative rather than analgesic action, and 3, 6, 5-trialkyluracils (R3, R5 : C4H9, R6 : CH3) showed a comparatively strong sedative action.