A digital broadcast transmitting and a method of processing broadcast data in a digital broadcast transmitting system are disclosed. The method includes randomizing mobile service data; RS encoding and CRC encoding the randomized mobile service data to build an RS frame; dividing the built RS frame into L (L>1) number of portions and adding K bytes (K≧0) of dummy data to one of the portions; encoding data in the portions at a code rate of 1/H (H>1); first interleaving the encoded data; mapping the first interleaved data into data groups and adding known data sequences and transmission parameters to each of the data groups, deinterleaving data of the data groups; second interleaving the deinterleaved data; and transmitting a transmission frame including the second interleaved data.