The present technology relates to a data processing device and a data processing method that enable tolerance against error of data to be improved. In the case in which an LDPC code having a code length of DVB-S.2 of 16200 bits and an encoding rate of 1/3 is modulated by 16 QAM, if a code bit of 4×2 bits and a (i+1)-th bit from a most significant bit of symbol bits of 4×2 bits of two consecutive symbols are set to bits b#i and y#i, a demultiplexer performs interchanging to allocate b0, b1, b2, b3, b4, b5, b6, and b7 to y6, y0, y3, y4, y5, y2, y1, and y7, respectively. The present invention can be applied to a transmission system transmitting an LDPC code or the like.