In　this　paper,　we　propose　a　penalized　constrained　least　squares　method　for　variable　selection　in　semiparametric　isotonic　regression　model.　Under　certain　regularity　conditions,　asymptotic　properties　of　the　proposed　estimators　are　established.　A　simulation　study　is　presented　for　illustrations.　©　2011　Springer-Verlag　Berlin　Heidelberg.