In　this　paper,　protograph-based　quasi-cyclic　(QC)　low-density　parity-check　(LDPC)　codes　are　proposed　for　the　efficient　structure　coding　of　LDPC　codes　in　2-D　intersymbol　interference　(ISI)　ultrahigh　density　magnetic　recording　channels,　such　as　bit-patterned　magnetic　recording　and　2-D　magnetic　recording,　where　a　reduced-complexity　2-D　detector　based　on　the　iterative　row-column　soft　detection　feedback　with　Gaussian　approximation　is　employed　instead　of　the　full　2-D　Bahl-Cocke-Jelinek-Raviv　detector.　The　proposed　protograph-based　codes,　whose　base　matrices　are　constructed　according　to　the　degree　sequences　for　2-D-ISI　channels,　have　a　low-complexity　QC　encoder　structure　with　a　readily　parallelizable　protograph　decoder　structure.　Simulation　results　show　that　the　proposed　protograph-based　QC-LDPC　codes　outperform　the　random　LDPC　codes　optimized　for　additive　white　Gaussian　noise　channels.　Furthermore,　the　performance　of　the　QC　codes　is　similar　to　that　exhibited　by　ISI-optimized　random　LDPC　codes　designed　for　2-D-ISI　channels,　while　retaining　the　implementational　benefits.　©　1965-2012　IEEE.