Aconitum L. (Ranunculalceae) is a large genus of about 300 species distributed in the temperate regions of the Northern Hemisphere [1]. The plant Aconitum kongboense Lauener is endemic to China, and its roots are used for the treatment of arthritic pain in folk medicine [2]. In previous reports [2–8], eighteen C19-diterpenoid alkaloids were isolated from this plant. In this paper, we report the isolation and structure elucidation of fifteen compounds from the chloroform extract of A. kongboense Lauener, including six C20-diterpenoid alkaloids (1–6), which were different from previously reported C19-diterpenoid alkaloids. The compounds were characterized by the comparison of the physical and spectroscopic data with the reported data, including NMR and mass spectrometry. The fifteen compounds were identified as: songorine (1) [9], karakomine (2) [10], 12-epi-15-O-acetylnapelline (3) [11], songoramine (4) [12], 12-epi-19-dehydronapelline (5) [13], 12-epi-19-dehydrolucidusculine (6) [13], 8,9,10-trihydroxythymol (7) [14], 8,10-dihydroxy-9-isobutyryloxythymol (8) [15], (+)-medioresinol (9) [16], ethyl caffeate (10) [17], estragole-3-O--D-glucopyranoside (11) [18], p-methoxysalicylic acid (12) [19], 2,4-dimethoxybenzoic acid (13) [20], scopoletin (14) [21], and wedelolactone (15) [22]. All of them were isolated from this plant for the first time.