The objective of the study was to assess the efficacy and tolerability of sodium valproate (VPA) on chronic daily headache (CDH) in a prospective, double-blind, randomized, placebo-controlled trial. Seventy patients were included in the study. Twenty-nine had chronic migraine ( CM) and 41 had chronic tension-type headache ( CTTH). VPA and placebo were applied for 3 months to 40 and 30 patients, respectively. Visual analog scale ( VAS) and pain frequency (PF) were used for evaluation. VPA decreased the maximum pain VAS levels (MaxVAS) and PF at the end of the study ( P = 0.028 and P = 0.000, respectively), but did not change general pain VAS (GnVAS) levels ( P = 0.198). In CM patients, the decreases in MaxVAS, GnVAS and PF parameters were more in VPA treated patients ( P = 0.006, P = 0.03, and P = 0.000, respectively). VPA treatment caused more reduction in PF than placebo in the CTTH subgroup ( P = 0.000). VPA is effective in the prophylactic treatment of CDH by reducing MaxVAS levels and PF. It was more effective in CM than in CTTH.