Abstract: AimTo get some novel potent compounds with NOS inhibitory activity, a series of new compounds of isothioureas derived from 1,2,3,4-tetrahydroisoquinoline were synthesized. Methods1,2,3,4-Tetrahydroisoquinol-2-yl was introduced into the structure of isothioureas, the NOS inhibitory activity of the new compounds synthesized were measured. Results and ConclusionTwenty-two isothiourea derivatives of ［alkyl(or aryl)imino］ (1,2,3,4-tetrahydroisoquinol-2-yl)methyl alkyl thioethers (I) and S-alkyl-1-phenyl-3-［4-(1,2,3,4-tetrahydroisoquinol-2-yl)methane］phenyl isothioureas (II) were synthesized from thioureas by S-alkylation with alkyl halides, and their structures were identified by IR, ¹H NMR, MS and elemental analysis. The preliminary biological test showed that the part of type I (I-9 and I-13) had higher NOS inhibitory activity than that the control aminoguanidine (AG), but the type II had weak ability to inhibit NOS.