The respiratory quinones of an alkalophilic Bacillus sp. S1-3 were investigated. Quinones of the B. S1-3 were extracted and purified by reverse-phase partition high performance liquid chromatography (HPLC) following thin-layer chromatography. Similar to other members of the genus Bacillus, the B, S1-3 also contained menaquinones as a sole respiratory quinone. However, the main menaquinone type produced by B. S1-3 was the menaquinone with six isoprenoid units (MK-6) instead of MK-7, which is believed to be the main menaquinone type found in the genus Bacillus.