The longitudinal spin transfer, DLL, from high energy polarized protons to Λ and Λ̄ hyperons has been measured for the first time in proton-proton collisions at s=200GeV with the STAR detector at the Relativistic Heavy Ion Collider. The measurements cover pseudorapidity, η, in the range |η|<1.2 and transverse momenta, pT, up to 4GeV/c. The longitudinal spin transfer is found to be DLL=-0.03±0.13(stat)±0.04(syst) for inclusive Λ and DLL=-0.12±0.08(stat)±0.03(syst) for inclusive Λ̄ hyperons with η =0.5 and pT=3.7GeV/c. The dependence on η and pT is presented. © 2009 The American Physical Society.