Castor ( Ricinus communis L.) is an important oil crop in the spurge family. The seeds contain an oil with unique chemical properties for industrial uses. With the development of economy the demand of castor bean and castor oil is increasing rapidly, but the castor bean production is suffering a lot from the low-yield variety because of the lack of new breeding method. Genomic simple sequence repeat (SSR) marker is particularly valuable and convenient in studies of genetic diversity, evolution, QTL mapping. because of its co-dominance, reproducibility, abundance and extensive genome coverage, but few were exploited in castor. So far, there is no genetic map of castor to be used, which severely hampered the genetic researches in castor. In this study, a total of 2, 719 castor SSR markers were developed from the genome sequencing information and a SSR genetic linkage map was constructed with 3 different F 2 populations derived from the cross combinations YC2 × YF1 and YC2 × YF2 respectively. It was revealed that the SSR density in castor genome was approximately 15.81 SSR/Mbp and the frequency of SSR motifs decreased with the increased repeat unit size, the dinucleotide and trinucleotide repeats, with (AT)n and (AAT)n as the most common repeat unit respectively, dominated the SSR types. After integration, the linkage map consisted of 331 markers, including 317 SSR markers, 7 SRAP markers, 3 SSRAP markers, 3 morphological markers and 1 ISSR marker, distributed on 10 linkage groups, encompassing 1164.73 cM of genome, with an average marker interval of 3.63 cM. This is the first genetic linkage map of castor which is expected to facilitate the researches on genetics and breeding in castor as well as the comparative genomics research in the spurge family. [ABSTRACT FROM AUTHOR]