IBrain functions can be affected by the dietary precursors of neurotransmitters. Tryptophan (TRP) is the precursor of serotonin (5-Hydroxytryptamine; 5-HT) neurotransmitter that plays an important role in sleeping, mood, eating behavior, consciousness and cognitive functions. Present study describes the estimation of tryptophan in rat brain by aqueous-reverse-phase high performance liquid chromatography. Estimation was carried out on a shim pack end-capped C-18 column using water as mobile phase (pH=9 adjusted by addition of 0.1 mM NaOH) at a flow rate of 1 ml min-1. Eluents were monitored at 273 nm by an ultra-violet detector. The method was linear (R2=0.9973) and the limit of detection (LOD) and limit of quantification (LOQ) were 4.3920 and 13.3091 ng ml-1, respectively. The developed HPLC method is simple convenient, reliable and economical for the estimation of tryptophan in rat brain. In the present study, Albino Wistar male rats were randomly divided into two groups control and seaweeds treated rats. Seaweeds (Jolyna Laminiriodes) were orally given to test rats at a dose of 200 mg kg-1 whereas control rats were given vehicle for 28 days. After 28 days of treatment, rats were decapitated and its brain samples were taken out for the estimation of TRP. Current study observed increased in TRP levels in the brain samples of seaweed treated rats as compared to control rats. Therefore present study suggested the use of seaweeds in the treatment of disorders caused by TRP depletion. By this newly developed method for the estimation of TRP, effect of various drugs on TRP levels in the brain could be studied.