Objective To study the effect of potassium alginate on the clinical manifestations of essential hypertension (EH) patients. Method One hundred and two EH patients were randomly divided into potassium alginate treated group and control group. Antihypertensive drugs were taken as usual. Patients in the treated group were given milk powder mixed with 3. 5 g potassium alginate while the patients in control group were given milk powder only for 50 consecutive days. Blood pressure， blood routine， liver function， renal function， blood sugar and blood lipids of each subject were determined. The clinical symptoms and adverse reactions were investigated with questionnaires. Results The blood pressure of the potassium alginate treated group were decreased step by step following the intake of potassium alginate，and the blood pressure decreased significantly from the 21st day (P < 0. 05) of the trial. After taking potassium alginate for 50 days，the decrease of systolic and diastolic pressure in the treated group was at an average of 13. 89 mmHg and 10. 15 mmHg respectively，and the effective power of lowing blood pressure was 60. 78% . The scores of main clinical symptoms were significantly improved in the potassium alginate treated group，such as headache，dizziness，palpitations，tinnitus， insomnia，malaise of knee and waist，and the total efficiency was significantly different between the treated and control group. The total efficiency of improvement was 76. 47% . Conclusion Potassium alginate is effective in assisting antihypertensive drugs for decreasing blood pressure and alleviating clinical manifestations of essential hypertension patients.