The Effect of pressure on the superconducting transition temperature of Yb doped Ce 0.6Yb 0.4FeAsO 0.9F 0.1 has been investigated for the first time using resistivity and magnetization studies. Increase in chemical pressure by substitution of smaller Yb 3+ ions in place of Ce 3+ ions results in a significant enhancement of T c from 38 K (Yb free) to 47 K (40% Yb). Enhancement in T c with external pressure has been observed for this compound up to a maximum value of T c = 48.7 K at 1 GPa, beyond which T c starts decreasing monotonously. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) In this Letter the effect of pressure on the superconducting transition temperature for a newly synthesized iron arsenide compound, Ce 0.6Yb 0.4FeAsO 0.9F 0.1, is described. Substitution of smaller Yb 3+ ions in place of Ce 3+ ions results in an enhancement of T c from 38 K (Yb free) to 47 K (40% Yb). Using resistivity and magnetization studies, the enhancement of T c has been observed up to 1 GPa beyond which T c starts to decrease monotonously. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.