The present technology relates to a data processing device and a data processing method which can ensure high communication quality in data transmission using LDPC codes. In group-wise interleaving, an LDPC code having a code length N of 64800 bits and a coding rate r of 13/15 is interleaved in a unit of a bit group of 360 bits. In group-wise deinterleaving, a sequence of bit groups of the LDPC code which has been subjected to the group-wise interleaving is returned to an original sequence. The present technology can be applied to, for example, a case in which data transmission is performed using LDPC codes.