{10\bar11} transformation twins, produced in the martensite of commercially pure titanium, have been investigated by means of transmission electron microscopy and discussed in relation to the character of the martensitic transformation. The results are as follows: (1) The twins have a thickness of 250∼3000 Å, and they are different in appearance from those of the martensite of ferrous alloys. (2) The incoherent boundary of those twins was found to be (12\bar31), (0\bar223), or (11\bar20). From the angles between the coherent boundaries composing nodes, it is concluded that these boundaries cannot exist in thermal equilibrium, and consequently they show configurations resulting from the martensitic transformation. (3) It is considered that the (\bar1011) twin plane has come from (101)_β of the matrix, and therefore the twin plane must have played an important role in the transformation.