A series of novel N0 -arylidene-2-[1-(naphthalen-1-yl)-1H-tetrazol-5-ylthio] acetohydrazides was synthesized and evaluated, as nonnucleoside reverse transcriptase inhibitors (NNRTIs), for their in vitro HIV-1 and HIV-2 activity using the IIIB strain and ROD strain, respectively. The activity was monitored by the inhibition of the virusinduced cytopathic effect in the human T-lymphocyte (MT-4) cells. All of the new compounds were structurally confirmed by spectral analyses. Compounds 5q and 5r showed EC50 of 29.62 lM (CC50 of 169.24 ± 23.83lM) and 31.62 lM (CC50[309.06 lM), and resulting in selectivity index of 6 and [9, respectively. However, all newly synthesized derivatives were not active against HIV-2 replication.