New series of selenolo[2,3-c]pyridazine and pyrimido[4',5':4,5]selenolo[2,3-c] pyridazine derivatives were prepared from new 4-cyano-5,6-diphenylpyridazine-3(2H)selenone (2). Elemental analysis, IR, 1H NMR, 13C NMR and mass spectral data confirmed the structure of the newly synthesized compounds. Some selected compounds 2, 4a,b, 6a-c, and 11a were investigated for their anti-inflammatory activity. Compounds 4b and 6a-c which showed activity comparable to the standard drug Indomethacin were screened for their analgesic activity. In addition, the most active compounds were tested for their acute toxicity. Moreover, some of the tested compounds 4b, 6a, 6b and 6c were screened for their antibacterial and antifungal activities.