Abstract: Using the software of PCRDESN,two pairs of primers, R16mF2/ R16 mR2 and R16 F2/ R16R2, were designed based on the 16S rDNA sequence of Phytoplasma from Michigen Aster yellows(MIAY), Elm yellows(EY),Canadian peach X_disease(CX),Jujube witches’ broom(JWB)and Cherry lethal yellow(CLY) published in references. DNAs as templates were extracted from sweet potato midrib infected with or without Phytoplasma. Phytoplasma in sweet potato witches’ broom was detected using PCR and Nested_PCR. A Phytoplasma_specific 1.5 kb fragment and a 1.2 kb special fragment were amplified with PCR and Nested_PCR, respectively. The minimal amount of DNA extracted from the infected sweet potato for molecular detection using PCR and Nested_PCR were 107.3 pg/μl and 0.01073 pg/μl. It is showed that the methods of PCR and Nested_PCR were very sensitive, rapid and reliable in detecting sweet potato disease associated with Phytoplasma. Furthermore, Nested_PCR based on the PCR was more sensitive than PCR about 10000 times in detecting phytoplasma in sweet potato witches’ broom. The conclusion is that the molecular detection of Phytoplasma in sweet potato witches’ broom is a better method nowadays.