Lanthanide-catalyzed addition of diethylphosphite with chalcones was achieved under mild conditions. The reaction exhibited good product selectivity using different catalysts. γ-Oxophosphonates were obtained in high yields in the reactions catalyzed by Yb(OAr)3(THF)2, while those catalyzed by [(Me3Si)2N]3La(μ-Cl)Li(THF)3 afforded 1,2-oxaphospholane-5-phosphonates as the main products in moderate to