ABSTRACT1,3‐Diphenyl‐1H‐pyrazole‐4‐carbaldehyde (1) reacted with aniline, 2‐substituted anilines, and P,P‐dimethylphosphinic hydrazide in the presence of diethyl phosphite to give acyclic α‐aminophosphonate 2, cyclic α‐aminophosphonates 4–6, and α‐hydrazinophosphonate 7, respectively. Also, treatment of aldehyde 1 with cyanoaceto‐hydrazide, acetophenone, and malononitrile afforded the condensation products 8, 16, and 21, respectively, which in turn, reacted with diethyl phosphite and P,P‐dimethylphosphinic hydrazide. The reaction of diethyl phosphite with the hydrazone 8 and chalcone 16 yielded the novel phosphorus heterocycles 13 and 18, respectively, while its reaction with the dicyanoarylidene 21 produced the dicyanopyrazolyl phosphonate 22. On the other hand, treatment of the hydrazone 8 with P,P‐dimethylphosphinic hydrazide gave the unexpected P,P‐dimethylphosphinic hydrazone 15, which reacted with diethyl phosphite forming α‐hydrazinophosphonate 7. Furthermore, the interesting N‐phosphoryl pyrazoles 20 and 24 were resulted in good yield via cycloaddition of P,P‐dimethylphosphinic hydrazide to the chalcone 16 and dicyanoarylidene 21, respectively. Structures of all newly synthesized compounds were confirmed by considering the data of IR spectroscopy, MS, and 1H‐, 13C‐, and 31P‐NMR spectroscopy, as well as that of elemental analyses.