Aconite root has high toxicity caused by diester alkaloids, thus it was necessary to define the limiting value of diester alkaloids used in medicine formulation. To give the quality of ''Processed Aconite Root'' and ''Powdered Processed Aconite Root'' in the Japanese Pharmacopoeia (14th edn, supplement II), we established the official specification and evaluation methods of standard substances. High qualitative grade diester alkaloids, aconitine, hypaconitine, jesaconitine and mesaconitine, which were useful to evaluate the purity of processed aconite root and powdered processed aconite root, were prepared and evaluated for their stability. We studied the physicochemical specification and evaluation methods of these alkaloids. In addition, an ''Aconitum diester alkaloids standard solution for purity'', which was used for the purity test, was prepared, and we also studied its physicochemical specification and evaluation methods. In addition, to evaluate the quality of processed aconite root and powdered processed aconite root, a TLC identification test was established. A monoester alkaloid of benzoylmesaconine hydrochloride was used as the reference standard in the latter test, and we also investigated its physicochemical specification and evaluation methods.