Objective To evaluate the efficacy and safety of double dosage Tamsulosin in treating patients with type Ⅲ prostatitis.Methods According to the results of prostate secretion(EPS) examination and the national institute health-chronic prostatitis symptom index(NIH-CPSI) questionnaire,120 patients with type Ⅲ prostatitis were recruited and randomly divided into single dosage group (n =60),treated with 0.2 mg Tamsulosin and placebo once daily for 12 weeks,and double dosage group (n =60),treated with 0.4mg Tamsulosin once daily for 12 weeks.Before treatment,the NIH-CPSI total scores in single and double dosage group were 26.91 ± 4.08 and 27.31 ± 4.98,respectively.The pain index in each group was 10.64±2.23 and 11.47 ± 3.00,respectively.The voiding index was 6.52 ± 2.24 and 6.41 ± 2.97 respectively.In those groups,the quality of life index was 9.68 ± 1.81 and 9.45 ± 1.79,respectively.All those items didn't show significant difference among those groups (P ＞ 0.05).The patients were follow-up and evaluate by those items on weeks 12.Results Because of losing during follow-up,4 patients were excluded from single dosage group.2 patients were excluded from double dosage group.After treatment in single dosage group,the NIH-CPSI total scores were 12.11 ± 3.60,pain index were 3.57 ± 1.67,voiding index were 2.88 ± 1.70,quality of life index were5.59 ± 2.06.After treatment in double dosage group,the NIH-CPSI total scores were 9.90 ± 4.15,pain index were 3.21 ± 2.21,voiding index were 2.21 ± 2.11,quality of life index were 4.50 ± 1.97.After 12 weeks treatment,the NIH-CPSI total scores,pain index,voiding index,quality of life index in both two groups were improved (P ＜ 0.05),and the double dosage group improve better(P ＜ 0.05).In the course of treatment,there were 2 cases of patients (3.8％) with adverse drug reactions in single dosage group,including dizziness in 1 case,headache in 1 cases.There were 4 cases of patients (6.9％) with adverse drug reactions in double dosage group,including dizziness in 3 cases of and rhinitis in 1 case.The rate of adverse reactions had no significant differences in the two groups (P ＞ 0.05).Conclusions Compared with single dosage Tamsulosin in the treatment of type Ⅲ prostatitis,double therapy had a better efficacy.Double dosage Tamsulosin therapy had an equal safety to the single dosage Tamsulosin.