Data comprise results of systematic live-trapping surveys of small mammals on three types of arable field margin at 30 locations on the Hillesden Estate, Buckinghamshire (UK), for four autumn and four spring periods between 2005 and 2011. Trapping was conducted on standard (cross compliance) field margins, and also on conservation margins (Entry Level Scheme). Data include 3172 trap records of animal captures, including breeding condition, mass (g), and recaptures. Dominant species are Wood Mouse (Apodemus sylvaticus), Bank Vole (Myodes glareolus), Field Vole (Microtus agrestis) and Common Shrew (Sorex araneus), with smaller numbers of Pygmy Shrew (Sorex minutus), Water Shrew (Neomys fodiens) and Harvest Mouse (Micromys minutus). The research was funded by Defra.