Background: Both hypokalemia (hypoK) and hyperkalemia (hyperK) are life-threatening to hemodialysis (HD) patients. This study was conducted to compare their clinical characteristics and long-term survival. Methods: Patients were divided into three groups according to the last mid-week predialysis serum potassium concentrations: hypoK (<3.5 mEq/l), normoK (between 3.5 and 5.5 mEq/l), and hyperK (>5.5 mEq/l). The maximal duration of the follow-up period was 54 months. Results: Compared with the hyperK group,patients in the hypoK group were older (p <0.05), had a higher incidence of comorbidity factors, less body weight gain prior to HD (p < 0.05), lower body mass index (BMI, p < 0.05), and higher BUN to creatinine ratio and hs-CRP (p < 0.05). The serum albumin and prealbumin concentrations were also lowest in the hypoK group, compared with the normoK and hyperK groups, respectively (all p < 0.001). A similar finding was also obtained for the normalized protein catabolism rate (nPCR, p < 0.001) among the three groups. Positive linear correlations between serum albumin and potassium concentration were only found in the hypoK and normoK groups (p < 0.001). Multiple logistic regression analysis showed that hypoalbuminemia, low BUN, and phosphate concentrations were significantly correlated with hypoK. HypoK patients also had a lower cumulative survival rate than hyperK patients. Conclusion: HypoK HD patients, with lower serum levels of albumin, prealbumin, nPCR, and BMI, but higher level of hs-CRP, showed a malnutritional and inflammatory status, and caused increased mortality rate.