To study the effect of S on the second phase particles (SPPs) of zirconium alloys, alloy samples were prepared by adding different contents of S (26~570 μg/g) into Zr-0.70Sn-0.35Nb-0.30Fe alloys. SEM and TEM with EDS were used to investigate the composition and crystalline structure of SPPs. The results show that in Zr-0.70Sn-0.35Nb-0.30Fe alloy, there exists Zr(Nb,Fe)2 SPPs with hexagonal close packed structure, while in the alloys containing S, orthogonal Zr3Fe SPPs appear besides Zr(Nb,Fe)2 SPPs and the Zr3Fe SPPs increase in amount with increasing S content. Zr9S2 SPPs occur when the S content reaches 190 μg/g, and also increase in amount with further increasing S content. The ratio of Nb/Fe decreases with the increase of SPPs’ size in the same zirconium alloy. It is indicated that the S content dissolving in α-Zr matrix is between 26 mg/g and 190 mg/g for the alloys in this study and the excess S dissolving in α-Zr matrix is precipitated as Zr9S2 SPPs rather than entering into other SPPs.