Background and objectives: People with refractory epilepsy on Valproic acid monotherapy, need safer and more effective therapy. Clobazam is frequently used as a supplement to treat drug-resistant epilepsy. But data regarding efficacy and safety of Clobazam as add on therapy is scarce. The present study was conducted to estimate the efficacy of Clobazam as first add on therapy along with Valproic acid in treatment of GTCS, in the form of reduction of seizure frequency and to identify the adverse drug reactions as add-on medication for the treatment of refractory GTCS not managed with valproic acid monotherapy. Methods: An observational prospective study was conducted among 113 Neuromedicine OPD attendees who were aged ≥18 years, suffering from GTCS and was on Valproic acid monotherapy but not responding. Patients were recruited for 4 months with two follow ups in 3 months interval. Data related to baseline parameter, seizure frequency, blood parameter were collected in all visits using a pre-designed, pre-tested, structured interviewer-administered questionnaire. Analysis was done using statistical software SPSS 20.0. One way repeated measured analysis of variance (ANOVA) with post hoc Bonferroni, Friedman test, Cochran's Q test with post hoc McNemar was conducted. p value ≤ 0.05 was considered as significant with 95 % confidence. Results: Mean (±SD) age of the study participants was 37.69±11.54 years. Seizure frequency was decreased from 1st visit to 3rd visit. Body weight of the participants increased in successive visits [Wilk's Lambda =0.528, F (2, 99)=44.178, p < 0.05, ƞ2=0.472]. Frequency of somnolence was increased over time (Cochran's Q=119.011, p=0.000). Conclusion: Clobazam is a very effective add-on drug for control of refractory GTCS patients who are on Valproic acid monotherapy. Clobazam has good safety and efficacy profile as an add-on drug.