Abstract: Objective To evaluate the diagnostic value of the seated saline suppression test（SSST） and its optimal cutoff point on the diagnosis of primary aldosteronism（PA）. Methods The clinical data of 242 patients at high risk of PA between September 2018 and September 2019 were analyzed. All patients underwent both SSST and the fluorocortisone suppression test（FST）. Plasma aldosterone concentration（PAC）≥60 ng/L after FST was taken as the "gold standard" for PA diagnosis. The diagnostic efficiency and the optimal cutoff of SSST were analysed by using the receiver operating characteristic（ROC） curve. Results In 242 patients, 163 were diagnosed with PA and 79 with essential hypertension（EH）. The area under ROC curve（AUC） of PAC post-SSST was 0.861（0.810-0.902）. When the cutoff of PAC post-SSST was set at 60 ng/L, the specificity and sensitivity were 43.04% and 91.41%, respectively. When the cutoff of PAC post-SSST was set at 85 ng/L, the specificity and sensitivity were 87.34% and 72.39%, respectively. Conclusions PAC post-SSST is a reliable parameter for the diagnosis of PA. PA can be excluded if PAC post-SSST is ＜60 ng/L. PA is highly likely if PAC post-SSST is ＞85 ng/L. A grey zone of PAC post-SSST existing between cut-offs was 60-85 ng/L.