Reaction of 2-chloro-5-heptadecyl[l,3,4]thiadiazole(3) with acetylhydrazine, o-phenylenediamine, anthranilic acid, and sodium azide produced a bridgehead nitrogen compounds(4-7) respectively. While reaction of(3) with piperidine produced (8). When 2-hydrazino-5-heptadecyl[l,3,4]thiadiazole (9) was reacted with β-benzoylpropionic acid, β aroylacrylic acid and phthalic anhydride produced 2-(5-heptadecyl[l,3,4]thiadiazol-2-yl) -6-phenyl-4,5-dihydro-2H-pyridazin-3-one (10) , 6-(4-chloro-3-methyl-phenyl)-2- (5-heptadecyl[1,3,4]thiadiazol-2-yl)-2H-pyridazin-3-one (11), and 2-(5-heptadecyl [l,3,4]thiadiazol-2-yl)-2,3-dihydro-phthalazine-l,4-dione (12) respectively. The biological activity of the synthesized compounds (including structure-activity relationship (SAR) study) was screened in vitro against some bacteria and fungi. Tetracycline was taken as standard antibacterial agent, and Amphotericin B as standard antifungal agents. Some of the synthesized compounds revealed high antibacterial and moderate antifungal activities. Propoxylation of compounds 1,9 and 12 with 3,5,7 moles of propylene oxide produced new class of nonionic surfactants I(a-c)-III(a-c) having surface active properties so, it was clear that the tested surfactants can be used in manufacture of dyes, drugs, cosmetics, emulsifiers, pesticides, luminphores for optical applications and many other industries with low toxicity to human being and environment owing to their high solubility and good biodegradability.