The present technology relates to a data processing device and a data processing method capable of securing excellent communication quality in data transmission using an LDPC code. In group-wise interleave, an LDPC code having a code length N of 64800 bits and a coding rate r of 9/15, 11/15, or 13/15 is interleaved in units of bit groups of 360 bits. In group-wise deinterleave, a sequence of LDPC codes after the group-wise interleave is returned to an original sequence. The present technology, for example, can be applied to a case where data transmission using an LDPC code or the like is performed.