Abstract: Second phase particles（SPPs） in N36 zirconium alloy claddings and bars was studied by SEM and TEM equipped with EDS. The result showed that SPPs in the claddings and the bars nearly have the same average diameter, but have different morphology and distribution. Zr（Nb,Fe）₂ Laves phase and a few of β-Nb phase precipitates were detected both in N36 alloy claddings and bars by diffraction and EDS analysis, but Laves phase in the bars had lower Nb content and smaller crystal lattice than that in the claddings. This study also illuminated that Nb content in α-Zr matrix for the cladding approaches to the solubility limit which appears equal to 0.3 wt~0.4 wt%, which is much lower than the usually assumed value of 0.6 wt%.