Abstract: The field trial on the effect of Gesaprin on controlling weeds and the safety to corn in spring corn fields was conducted during 1999~2000. The results showed that 90%gesaprinWP could control effectively broadleaf weeds in spring cornfield, such as Bacon weed (Chenopodium album L.), Willow leaf knotweed (Polygonum bungeanum Turcz.), Redroot pigweed (Amaranthus retroflexus L.) and Black nightshade (Solanum nigrum L.). But the control effects of Gesaprin to Heartleaf cocklebur (Xanthium strumarium L.), Velvetleaf (Abutilon theophrasti Medic.) and the grass family were poorer. The control effects of weed plant and weed fresh weight were over 90%. The optimum application timing was in after planting and pre-germination. The suitable dosage was 90% Gesaprin WG 1620~1890(g·ai)/hm2. These dosages were safe to spring corn.