Objective: To compare the contents of heavy metals, residual pesticides and sulfur dioxide before/after a decoction. Methods: The heavy metal contents before/after a decoction were measured by inductively-coupled plasma atomic emission spectrometer (ICP-AES) and mercury analyzer. In order to analyze pesticides in 5 samples we used simultaneous multi-residue analysis of pesticides by GC/ECD, which was followed by GC/MSD analysis to confirm the identity of the detected pesticide in each sample. In addition, the contents of sulfur dioxide ($SO_2$) were performed by Monier-Williams distillation method. Results: 1. The mean values of heavy metal contents (mg/kg) for the samples were as follows: Sipjeondaebo-tang (before decoction - Pb; 1.163, Cd; 0.257, As; 0.080 and Hg; 0.016, after decoction - Pb; 0.059, Cd; 0.007, As; 0.006 and Hg; 0.0003), Palmul-tang (before decoction - Pb; 1.181, Cd; 0.242, As; 0.152 and Hg; 0.014, after decoction - Pb; 0.067, Cd; 0.008, As; 0.008 and Hg; 0.0003), Sagunja-tang (before decoction - Pb; 1.285, Cd; 0.283, As; 0.063 and Hg; 0.012, after decoction - Pb; 0.047, Cd; 0.009, As; 0.004 and Hg; not detected) and Samul-tang (before decoction - Pb; 1.025, Cd; 0.169, As; 0.099 and Hg; 0.013, after decoction - Pb; 0.065, Cd; 0.007, As; 0.010 and Hg; 0.001). 2. Contents (mg/kg) of residual pesticides before/after a decoction were not detected in any samples. 3. Contents (mg/kg) of sulfur dioxide ($SO_2$) before a decoction in Sipjeondaebo-tang, Palmul-tang, Sagunja-tang and Samul-tang exhibited 5.0, 6.0, 14.0 and 6.9, respectively. However, contents of sulfur dioxide after a decoction were not detected in any samples. Conclusion: These results will be used to establish a criterion for heavy metals, residual pesticides and sulfur dioxide.