Abstract: 2-(5-Mercapto-4-phenyl-4H-[1,2,4]triazol-3-ylmethyl)-6-p-tolyl-4,5-dihydro-2H-pyridazin-3-one (3) was prepared according to the established sequenced procedures 1-3 . Subsequently by using selected alkylating agents; compounds 4a-c were prepared via regioselective S alkylation procedure4. Alternatively, compounds 5a-c were prepared via regioselective addition procedure 4 . Under Mannich condition, some interesting compounds 7a,b and 8a,b were successfully prepared. On the other hand, the azides 10 and 15 coupled with amino acid esters 11a-d and 15a- d to give amino acids derivatives 12a-d and 16a-d in good to moderate yield respectively. The structural elucidation of products is reported and also some of the products were screened for their antimicrobial activity.