The characteristics of the two’),—type phase transitions in solid deuteron-methane(CD 4) were studied by the neutron powder diffraction technique. The temperature—dependence of the integrated intensity of certain low—angle peaks which disappear after the completion of the phase transitions, together with the temperature-dependence of the width-at-half height and of the angular positions of some peaks were obtained (both on warming up and cooling down the specimen). As a result, the following conclusions were drawn: The lower transition, which is completed at about 22.1 ± 0.15 K, was found to be a sharp first—order transition, such as one would expect for a transition involving change of symmetry. By Contrast, the upper transition, which is completed at about 27.0 ± 0.15 K, was found to be a gradual second-order type of transformation such as one expects for transitions which do not involve changes of symmetry. These observations are consistent with the structures of the low, middle and high phases of solid CD4 which are tetragonal, cubic and cubic respectively.