A 100 kDa protein was identified by a combination of microtubule affinity chromatography and microtubule co-sedimentation from Xenopus egg extracts. The 100 kDa protein was expressed in Stage VI oocytes and early embryos, and then decreased at tailbud stage. The 100 kDa protein was found in adult organs such as brain and liver. Immunofluorescent microscopy revealed that the 100 kDa protein was mainly detected in spinal cord, notochordal sheath, optic cup, lens and cement gland in tailbud embryos. In Xenopus A6 cells, the 100 kDa protein showed filamentous networks in the peripheral cytoplasm and uniform distribution around the nucleus. During cell division, the 100 kDa protein was localized to the mitotic apparatus. The 100 kDa protein may have some roles in microtubule dynamics, organization of the mitotic apparatus and maintenance of cell shape.