Objective: To explore the reporting of information useful in quality judgment and assess the external validity based on a sample of hypertension randomized controlled trials (RCTs) conducted in China. Methods: Four databases including the Cochrane Library, MEDLINE, CBMdisc (China Biomedicine Database Disc) and CNKI (Chinese National Knowledge Infrastructure) were searched between January 1996 and December 2006 for all hypertension RCTs conducted in China. Language was limited to Chinese and English. The internal validity of all RCTs was evaluated firstly by a modified scale, trials that fulfilled the minimum quality threshold were included. Information useful in assessing the internal validity and external validity was collected by using a data extraction form. Results: 164 RCTs were finally included for more informed assessment of external validity. (1) Representation of samples: 122 (74.4%) RCTs selected secondary or tertiary cares as their trial settings. 81 (49.4%) RCTs described the source of samples, in which 86.3% patients came from hospitals, only 13.7% came from communities. 24.6% patients were ineligible for inclusion criteria in 8 (4.9%) RCTs, 14.5% eligible patients were non-enrolled in 2 RCTs, 16.7% patients in 12 (7.3%) RCTs were excluded in run-in periods. The elderly and women patients were markedly under-enrolled in study population (P & 0.001), participants in study population were younger, more often male, and the under-enrollment of women in study population was significantly associated with the mean age of participants in trials (P & 0.001). We also found that those RCTs funded by pharmacy and treated with a-Blocker more excluded patients aged 65 years or older (P & 0.05). (2) Intervention: Those RCTs with ARB were the most number (25%), next was the CCB(21%), the least was the diuretic, only 3%. (3) Outcome: Many RCTs had the inadequate duration of treatment follow-up, only 4 8 weeks. 6 RCTs choose the incidence or fatality of cardiocerebrovascular as the outcome, 12 RCTs choose the patient-centered outcomes. Only one RCT made the cost analysis. 96 RCTs (58.5%) described the adverse clinical events. Conclusion: The reporting of information useful for assessing the external validity in hypertension RCTs conducted in China was poorly addressed; there is marked room for improvement in quality of reporting. The elderly and women patients were consistently underrepresented in those RCTs, which might seriously affect the external validity of trials. The regulatory agencies of clinical trials in China should play an important role in both improving representation of study population and raising awareness of external validity in clinical trials.