Four 5-benzyl-1,3,4-thiadiazol-2-amine derivatives were synthesised from phenylacetic acid derivatives. The structures of the 5-benzyl-1,3,4-thiadiazole derivatives were characterised by NMR spectroscopy and X-ray crystallography. The acetylcholinesterase-inhibition activities were also tested. Among the four compounds, 5- (4-bromobenzyl)-1,3,4-thiadiazol-2-amine showed the best acetylcholinesterase-inhibition activity with an IC50 of 49.86 μM. The docking study performed with AUTODOCK demonstrated that this compound could interact with the catalytic active site of acetylcholinesterase.