In order to define the structural requirements of quinazoline-2(1H)-thiones 1 for their inhibitory activity on melanogenesis, a novel series of 3,4-dihydroquinazoline-2(1H)-thiones (3a-h) were prepared and screened for their melanogenesis inhibition on melanoma B16 cell line under the stimulant of alpha-MSH. The anti-melanogenesis activity of 3 is mainly mediated by the hydrogen bonding ability of thioamide unit in addition to complexation ability of thione and the hydrophobic binding power of side chain substitutions at 3-position. Thus, the pharmacophore of 3,4-dihydroquinazoline-2(1H)-thiones for their anti-melanogenesis activity could be refined as 3-hydrophobic substituted quinazolinethione.