Objective To compare the metabolic syndrome (MS) definitions from International Diabetes Federation (IDF) and the Chinese Diabetes Society (CDS) respectively,and to investigate their difference and agreement rate for diagnosis of MS in middle aged and elderly population in Guangzgou region. Methods In 2004,1270 Guangzhou shipyard workers and 2082 peasants from 4 villages of Dashi District,Panyu,Guangzhou with age ≥ 35 years,were investigated. They were asked to fill a medical history questionnaire and their height,weight,waist circumference,blood pressure,and blood biochemical markers were also measured. The individuals with incomplete data were excluded. Finally,1266 workers,and 1658 peasants were analyzed. MS prevalence rate in two groups were calculated following the definitions from IDF and CDS respectively. Results (1) A total of 40.5% individuals met the MS definition both from IDF and from CDS; 34.6% individuals only met the MS definition from IDF but not from CDS; 24.9% individuals only met the definition from CDS,but not from IDF. MS diagnosis agreement rate reached up to 87% (urban 87.3%,rural 87.1%). Kapple was 0.501 (P<0.001). (2) Using definition either from CDS or IDF,MS prevalence rate was roughly at the same level in urban (15.5%,IDF definition; 14.6%,CDS definition) and rural areas (16.6%,IDF definition; 13.8%,CDS definition). But according to the definition from IDF,there were 105 urban residents and 160 rural residents who did not meet the diagnosis of MS,because their waist index did not meet the standard although other three indicators did. (3) MS prevalence rate was higher with CDS definition (16.1%) than with IDF definition (12.3%) in male; but in female,it was higher with IDF definition (20.1%) than with CDS definition (12.0%). (4) After the subjects were divided into 5 different age groups,including <40 years,40-49 years,50-59 years,60-69 years,and >70 years respectively,it was found that MS prevalence rate increased with age. However,in>70 years group,MS prevalence rate decreased with age. The MS prevalence rate was the highest in 60-69 age group. Conclusion The MS definition from IDF and CDS can give identical MS prevalence rate. But men are more sensitive to the definition from CDS,while women to definition from IDF. The elderly individuals are the main targets for prevention and treatment of MS.