A trans-aconitate 3-methyltransferase (TMT1) is an enzyme that catalyzes the monomethyl esterification by transferring a methyl group to trans-aconitate, which is an intermediate in the citric acid cycle. While the TMT proteins use same substrate, the products could be varied depending on species. To understand how organisms utilize this enzyme in stressful environments and to increase its utility in producing a variety of substances, it is necessary to compare the structure and function of TMT1 in fungal species. To explore its structural and functional diversity, N-terminal His₆-tagged proteins from Kluyveromyces lactis was purified and crystallized. X-ray diffraction data were collected at a resolution of 1.7 Å. The crystal structure was determined to the space group P2₁2₁2₁, with unit cell parameters a = 46.6 Å, b = 56.3 Å, c = 109.1 Å, α = β = γ = 90°. The crystal contained one molecule per asymmetric unit.