A method of simultaneously screening 215 types of pesticides has been established by liquid chromatography with tandem mass spectrometry, quadrupole/time of flight mass spectrometry and triple quadrupole mass spectrometry. Samples of blood and gastric contents were prepared through the modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method. A modified QuEChERS that uses dispersive solid phase extraction for a small amount of sample, mini-QuEChERS, was applied to blood and gastric contents for quick and convenient preparation of the sample and to reduce matrix effect. This method of simultaneous identification needs the upmost reliability because these results are employed by forensic toxicology and may lead to issues with the law. In this study, we incorporated the following two concepts to demonstrate its reliability: One concept is that two tandem mass spectrometers are applied for the confirmation and then a precise compound identification is conducted synchronously at the same retention time. The other concept for reliability adopts the approved criterion as identification points, defined by EU. Validation of the method was performed to assess selectivity, linearity, limit of quantification (LOQ), and recovery by standard addition procedure. The result of linearity was almost satisfactory, and the LOQ of pesticides detected in whole blood and Korean characteristic gastric contents was between 2.5-50 ng/mL. About 90 % of the pesticides had 80-120 % recovery in whole blood, and about 78 % of the pesticides had 80-120 % recovery in Korean gastric contents.