Seeds and planting materials of different plant species are being imported into India. Many of these plants have the potential to become agricultural or environmental weeds and this risk needs to be assessed before allowing their entry. Weed risk assessment is a question based scoring system, containing 49 questions about the species. The questions include details of the plant’s climatic preferences, biological attributes, dispersal methods and reproduction. A minimum number of questions must be answered before an assessment is made. The weed risk assessment uses responses to the questions to generate a numerical score that is positively correlated with weediness. The assessment method was tested against 170 plants representing both weeds and useful plants from agriculture and environment. The method was judged on its ability to correctly reject weeds and accept non weeds. A total of 40% plants were classified as serious weeds, 30% as common weeds and remaining 30% were non weeds. The system is designed to be operated by plant quarantine officers. The weed risk assessment system with explicit scoring of biological, ecological and geographical attributes is a useful tool for detecting potentially invasive weeds in other areas of the world.