Objective To investigate the efficacy of stellate ganglion block (SGB) as treatment in primary dysmenorrheal (PD) patients and the possible mechanism. Methods A total of 76 PD patients were referred to our clinic from October 2007 to June 2011.All of them received SGB switching from left to right ganglion once daily from 7 days before through 3 days after menstrual period in 3 consecutive menstruation cycles.The visual analog scale (VAS) and sleep interference scale (SIS) were recorded within 24 hours after the last untreated menstruation (T0),the 1st treated menstruation (T1),the 2nd treated menstruation (T2),the 3rd treated menstruation (T3),and the 3rd menstruation after treatment (T4),respectively.In addition,the serum prostaglandin F2α (PGF2α) level and prostaglandin F2α/prostaglandin E2 (FGE2α/FGE2)ratio were measured at the above time points.Results The VAS scores at T1,T2,T3 and T4 were (1.83±0.52),(1.48±0.21),(1.25±0.14),(1.30±0.25),respectively,which were significantly less than that at T0 (6.35±1.42)(P＜0.01 ).The SIS scores at T1,T2,T3 and T4 were (1.52±0.41),(1.40±0.22),(1.12±0.11),( 1.33±0.24),respectively,which were significantly less than that at T0 (6.55±1.32) (P＜0.01).The serum PGF2α and PGF2α/PGE2 ratio at T1,T2,T3 and T4 were(5.1±1.1 ) μg/L and (2.1±1.3),(4.9±1.2),(1.9±1.4),(4.8±1.6) μg/L,(1.8±1.1),(4.9±1.7) μg/L and (2.1±1.3),respectively,which were significantly less than that at T0 (15.3±2.1),(5.2±1.6) (P＜0.01). Conclusions SGB is effective in pain relief and sleep improvement for PD patient,which may be associated with the reduction of serum PGF2α level and PGF2α/PGE2 ratio.