This study was carried out for establishment of toxicological monitoring system in oriental medicinal plants. Hence on our research, we used Banha(Pinellia ternata) and Kangbanha, Bubbanha, Jaebanha, Geokbanha by distinguished processing methods. These are frequently used in Bangyakhabpeon, which is one of the most well-known clinical book in oriental medicine. As we reviewed the reported documents, we judge homogentisic acid(HA) and 3,4-dihydroxybenzaldehyde(3,4-DBA) as poisonous substance and to verify its existence, we established analysis condition of HPLC by gaining sequential fraction extracts and studied the degree of its virulence to provide basic information on the guidelines of using this medicine. Optimum condition of HPLC was H₂O : MeOH : CH₃COOH (57:35:8) in HA and 3,4-DBA analysis. HA content of raw Banha was 11.03mg/100g and HA contents of its processed product were decreased. Exceptionally, Jaebanha was increased in 175.97% than raw Banha. 3,4-DBA content of raw Banha was 2.93mg/100g and 3,4-DBA contents of its processed product were decreased. These results will be applies in intake guideline establishment, quality control and stability evaluation of oriental medicinal plants.