Long-chain alkanes in the environment are more persistent and harder to degrade than short-chain alkanes. Geobacillus thermodenitrificans NG80-2, isolated from a deep subterranean oil-reservoir in the Dagang oil ﬁeld in Tianjin, China, is capable of degrading long-chain n-alkanes (C15-C36) via the terminal oxidation pathway. In the terminal oxidation pathway, alkanes are first attacked at the terminal methyl group by monooxygenases to give the corresponding primary alcohols, which are further oxidized by alcohol dehydrogenases and aldehyde dehydrogenases to fatty acids. Three types of enzymes in the terminal degradation pathway of the NG80-2 strain play important physiological roles in n-alkane degradation and bacterial growth in the oil field. The crystal structure of long-chain alkane monooxygenase (designated LadA) was previously reported. Here we determined the three-dimensional structures of the alcohol dehydrogenase (designated ADH2), the aldehyde dehydrogenase (designated ALDH), the complex of ADH2 with the NAD+ coenzyme and the complex of ALDH with NAD+ and Mg2+ by X-ray crystallography. The four structures together with the structure of LadA, representing the complete terminal oxidation pathway, reveal the mechanism of long-chain n-alkane degradation in thermophilic bacillus NG80-2. The results extend our understanding of the degradation mechanism and facilitate further study of the structure-function relationship of the alcohol and aldehyde dehydrogenases, thus providing a foundation for their application for in-site treatment for oil spills.