A series of 2-(substituted phenoxyacetoxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-ones IIa-s were designed and synthesized on the basis of the previous work for the modification of alkylphosphonates I, and their structures were confirmed by (1)H NMR, (31)P NMR, (13)C NMR, IR, MS, and elemental analysis. Their herbicidal activities against seven species of weeds were evaluated in a greenhouse. A part of the title compounds such as IIa-g, IIk, IIo, and IIr exhibited significant postemergence herbicidal activity against Abutilon theophrasti, Brassica juncea, Amaranthus retroflexus, and Eclipta prostrate at a dosage of 150 g ai/ha. Structure-activity relationship analyses indicated that the introduction of a phosphorus-containing heterocyclic ring had a favorable effect on herbicidal activity, and their herbicidal activity could be further increased by a reasonable combination of X, Y, and R in parent structure II. It could be found that the title compounds IIa 2-[(2,4-dichlorophenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one and IIr 2-[(4-chloro-2-methyl-phenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one possess high activity and a broad spectrum against all of the test broadleaf weeds with 70-100% inhibition effect at a dosage of 75 g ai/ha, and the title compounds IIa and IIr are safe for corn and wheat at a dosage of 150 g ai/ha. Furthermore, the title compound IIa possesses low rat toxicity. These results suggest that the title compounds IIa and IIr could be potential and selective postemergence herbicides for further development.