In this study,genetic diversity among 82 Amphobotrys ricinistrains (81 strains from castor bean Ricinus communis L. and copperleaf Acalypha australis in China,1 strain from USA) was studied based on RAPD technology. The results showed that eight RAPD primers produced 63 DNA bands in total,of which 49 DNA bands were polymorphic DNA bands with the percentage of polymorphic DNA bands (PPB) reaching up to 77.8%. Polymorphism information content (PIC) values ranged from 0.47 to 0.84 with a mean value of 0.72. The number of observation alleles (Na) was 2.000 0,the number of effective alleles (Ne) was 1.357 7,Nei’s genetic diversity index (H) was 0.227 5 and Shannon information index (I) was 0.363 1. UPGMA cluster analysis showed that genetic similarity (GS) ranged from 0.55 to 1.00 among the 82 investigated A. ricini strains. Samples could be divided into 5 groups (A,B,C,D,E) at the GS of 0.70 and B group could be divided into B1 and B2 subgroups at the GS of 0.74. The RAPD groups had a certain correlation with the geographical origin and the host of the strains. In summary,the study revealed the genetic diversity of the A. ricini population and its relationship with geographical origin and host.