A method and an apparatus for transmitting broadcast, signals thereof are disclosed. The method for transmitting broadcast signals includes processing input streams into BB frames in PLPs; encoding data of the PLPs; building at least one signal frame by mapping the encoded data of the PLPs; and modulating data in the built signal frame by OFDM method and transmitting the broadcast signals having the modulated data, wherein at least one of the BB frames includes a stuffing field and a first indicator describing whether the stuffing field is included in the BB frame.