Oxypnictides of types CeOFeAs1-xSbx, CeO 0.9F0.1FeAs1 - xSbx and CeO 0.8F0.2FeAs1 - xSbx have been synthesized in order to understand the effective change in electron doping by the twin effects of F- incorporation and the variation in Fe-As bonding by substitution of a larger ion (Sb) at the As site. All the compounds crystallize in a tetragonal ZrCuSiAs-type structure (space group: P4/nmm). Both the lattice parameters (a and c) increase with the increase in antimony substitution due to the larger ionic size of antimony. CeOFeAs 1 - xSbx (x = 0.1, 0.2 and 0.3) compounds were found to be semimetallic, like the parent CeOFeAs. Substitution of Sb in CeOFeAs 1 - xSbx results in a shift of the temperature of the resistance anomaly corresponding to the structural phase transition. CeO 0.9F0.1FeAs1-xSbx ('x' = 0, 0.05, 0.1 and 0.15) was superconducting with a maximum transmission temperature (Tc) of 43.17K for 'x' = 0.1, which is higher than the antimony-free CeO0.9F0.1FeAs (Tc= 38K). Further increase in antimony (x > 0.15) results in the suppression of superconductivity. Similarly, Sb doping in optimally electron doped CeO0.8F 0.2FeAs superconductor leads to the lowering of the superconducting transition temperature ('x' = 0.1) and further increase in antimony substitution ('x' > 0.1) leads to a loss of superconductivity. CeO0.8F 0.2FeAs0.9Sb0.1 shows a very high value of the upper critical field Hc2(0) (137T) as compared to Sb-free CeO 0.8F0.2FeAs. In this paper, we discuss the first example among electron-doped oxypnictide superconductors where the Tc increases as a result of a decrease in chemical pressure (an increase in lattice parameters). © 2011 IOP Publishing Ltd.