Interference　alignment(IA)　with　symbol　extensions　in　the　K-user　multiple-input　multiple-output　(MIMO)　interference　channel(IC)　is　considered　in　this　paper.　Symbol　extensions　produce　the　channels　of　special　structure.　Most　of　existing　approaches　are　limited　in　cases　where　the　channels　have　some　special　structure,　because　they　align　the　interference　without　preserving　the　dimensionality　of　the　desired　signal.　For　that　reason,　two　novel　iterative　algorithms　for　IA　with　symbol　extensions　are　proposed.　The　first　algorithm　designs　transceivers　for　IA　based　on　minimizing　the　maximum　per-user　mean　square　error(MSE)　while　preserving　the　dimensionality　of　the　desired　signal.　Utilizing　channel　reciprocity,　the　second　algorithm　is　proposed　which　is　the　constrained　optimization　problem.　It　maximizes　each　receiver＇s　SINR　while　preserving　the　dimensionality　of　the　desired　signal.　The　simulation　results　show　that　the　proposed　algorithms　not　only　achieve　good　performance　in　terms　of　BER　performance　but　also　achieve　good　performance　on　maximizing　sum　rate　of　the　system.　©　2012　IEEE.