SibL is an S-adenosyl-L-methionine (SAM)-dependent C-methyltransferase (CMT) involved in sibiromycin biosynthesis. Specifically, it establishes the C8 methylation step in the biosynthesis pathway, and the resultant methyl group is important for maturation of the antitumor antibiotic. Here, we purified and crystallized SibL from Streptosporangium sibiricum using the sitting-drop vapor-diffusion method. The crystals diffracted to a resolution of 2.9 Å and belonged to orthorhombic space group F222, with unit-cell parameters a = 102.93, b = 295.42, c = 322.23 Å. Determining the structure will provide insights into how SibL methylates 3-hydroxykynurenine (3HK).