In the process of discovering and identifying new factors that regulate the development of plant trichome, we obtained a recessive Arabidopsis thaliana mutant aberrantly branched trichome 31 (abt31).Compared to the wild type (Col0)A. thaliana, abt31 appeared a high proportion of multibranched trichomes.In addition, abt31 is dramatically reduced in size and has a defective primary root, wide shaped grey leaves. The mutant gene ABT3 was precisely mapped into the 134 kb chromosome interval between the molecular markers F28G11#3 and F4N21#1 on chromosome 1, which was determined using the position cloning strategy.This research will lay a foundation for further cloning ABT3 gene and studying its role in the regulation of plant growth and development.