Stabilization of the perovskite phase and sequence of reactions occuring during calcination were studied with solid solutions formed between Pb(Zn1/3Nb2/3)O3 and Pb(Fe1/2Nb1/2)O3. In the PZN-PFN composition of equal molar ratio, rhombohedral type pyrochlore phase (Pb2Nb2O7) and PbO-rich distorted cubic type pyrochlore phase (Pb3Nb2O8) were coexisted as intermediate phases at temperatures below 85$0^{circ}C$, and these phases transformed to a stable cubic type pyrochlore phase, Pb3Nb4O13 solid solution and a perovskite solid solution at temperatures above 85$0^{circ}C$. The major stable phase as increasing sintering temperatures was a perovskite phase in this binary system and prominent suppression of the pyrochlore phase was achieved by substituting Zn2+ with Fe3+ or by increasing sintering temperature. The composition containing 20mol% PZN possessed the best dielectric properties, and the dissipation factor was lower than 5% in all compositions.