Acetylation of 3-acetyl-4-aryl-2-pyrazolines (2) under the usual conditions of refluxing with acetic acid led to the decomposition of pyrazolines. However, acetylation with Ac2O/Py afforded the desired 1,3-diacetyl-4-aryl-2-pyrazolines (3) in 39-73% yield. 2a formed an adduct (4) with benzalacetone. Structures of the products have been established through interpretation of high resolution NMR, mass spectroscopic data.