Background: Gastroesophageal reflux disease and laryngitis are common diseases in Thai population. Since now, we found that acid reflux was one of the most common causes of laryngitis.  The term laryngophayngeal reflux (LPR) is used to describe esophageal acid reflux into laryngeal and pharyngeal areas.  Twenty-four-hour pH monitoring seems to be the best modality to establish LPR, although some caution should be concerned in the interpretation of these results.  Treatment of patient with suspected “reflux laryngitis” with antireflux medications has been shown to be effective.  Although limited double-blind, controlled study recently showed equivocal result in improvement among patients treated with PPIs versus placebo.Patients and Methods: This is a prospective, randomized, placebo-controlled, double-blind study to evaluate effect of rabeprazole for therapeutic trial in chronic idiopathic laryngitis.  Symptoms and laryngeal finding were assessed prior to and 12 weeks after randomization to rabeprazole or placebo group.Results: Thirty patients had qualified for the study.  In all cases, ambulatory, 24-hour, double probe pH monitoring and video laryngoscopy were done.  All enrolled patients completed the study.  There were 4 males and 11 females in both rabeprazole group and placebo group.  The most common symptoms were globus sensation (86.7%), excess throat mucous (80%), heartburn or regurgitation (70%).  The mean reflux symptom index (RSI) at the initial pretreatment visit was 11.4 and the mean RSI at the completion of the 12-week treatment period was 5.3. The mean RSI difference between pre and post treatment was 6.1 +/- 3.7.  When determined clinical response, the improvement of symptom score more than 60% from pretreatment, there was no statistically significance between rabeprazole and placebo group. (p = 0.143)  In subgroup of positive pH monitoring, RSI significantly decreased in rabeprazole group when compare to placebo. While in pH negative subgroup, rabeprazole improved symptom score without statistically significances when compared with placebo. (p >0.05) In general, symptom scores improved over time for patients in both groups.  There were no statistical differences between rabeprazole and placebo groups for symptoms improvement at 4 and 8 weeks therapy.  All patients underwent video laryngoscopy at pretreatment period.  Only 22 had undergone video laryngoscopy at the end of treatment. There was no differences in pretreatment and % improvement of RFS at the end of study between rabeprazole (7.4 +/- 2.8) and placebo group. (7.6 +/- 2.6) (p = 0.84)  In subgroup of previous medication used, rabeprazole can improve RSI symptoms 81.78%. There was no adverse reaction demonstrated in both groups.Conclusions: Rabeprazole improves clinical symptoms and laryngeal signs in LPR patients with positive 24-hour pH monitoring results.  24-hour pH monitoring is helpful in identification of patients likely to response to antireflux therapy.