Abstract: Vilsmeier-Haack reaction conditions were applied on some methyl ketone aryl phosphonic dihydrazones to yield some interesting bis-pyrazole derivatives containing a hydro-phosphoryl unit. Bis-{4-formyl-3-aryl-1H-pyrazol-1-yl}phosphine oxides (4a,b) were condensed with some nucleophiles such as aniline, phenacyl triphenylphosphonium bromide and 4-phenylthiosemicarbazide followed by treatment with thioglycolic acid, diethyl phosphite and/or acetic anhydride to yield a novel class of bis-pyrazoles containing sulfur and phosphorus derivatives. Most of the newly synthesized compounds were evaluated for their in vitro antimicrobial activities.