The present technology relates to a data processing device and a data processing method, which are capable of securing excellent communication quality in data transmission using an LDPC code. In group-wise interleave, an LDPC code in which a code length N is 16200 bits and an encoding rate r is 12/15, 6/15, or 8/15 is interleaved in units of bit groups of 360 bits. In group-wise deinterleave, a sequence of the LDPC code that has undergone the group-wise interleave is restored to an original sequence. For example, the present technology can be applied to a technique of performing data transmission using an LDPC code.