Series of compositions with general stoichiometry as Ca1-xZr1-xRE2xTi2O7 (RE= Nd3+, Sm3+) were prepared by solid state reaction and characterized by powder x-ray diffraction technique to unravel the phase fields in the title systems. The phase fields in CaZrTi 2O7-Nd2Ti2O7and CaZrTi2O7-Sm2Ti2O7 systems differed significantly at the rare-earth rich regions. The common phase fields like zirconolite-2M, zirconolite-4M, cubic perovskite are observed at the zirconolite rich regions of both systems. Depending on the structure of RE2Ti2O7 phase, the cubic pyrochlore or monoclinic RE2Ti2O7 phases are observed in the studied system. The observed phase fields in these two systems indicate ionic radius of the rare-earth ion has a dominating role in the phase relations. Further details of the phases and their homogeneity are explained in the text of the manuscript.