Hydrodynamic afterburner for the CGC at RHIC We take hydrodynamic initial conditions in relativistic heavy ion collisions from the Color Glass Condensate (CGC) picture through the $k_T$ factorization formula. Gluon distributions produced from the CGC are found to provide good initial conditions for the hydrodynamic simulations in Au + Au collisions at Relativistic Heavy Ion Collider (RHIC) energies. We reproduce the centrality, rapidity, and energy dependences of multiplicity within this approach. We also investigate the energy loss of high $p_T$ partons in the dense thermalized medium created from colliding two CGC's.