One approach to improve the photocatalytic activity of TiO2 catalyst is doping metal/metal ion on TiO2 catalyst. Usually metal elements are doped on single phase TiO2 catalysts and the content of dopant is usually larger than 1%. In this study, we dope trace ions of transitional metals, Co and Cu, and lanthanide metal Ce on the nanofibers of mixed anatase and TiO2(B). There have been limited studies on photocatalytic activity of TiO2(B) phase and no study on the doping on nanostructure of the mixed anatase and TiO2(B). The doping on the mixed phase systems could be very different from that on a single phase. The dopants may distribute preferably on one of two phases or in the interface region. This can effect the mechanism and activity photocatalytic reactions. Sulforhodamine-B (SRB) was used as a model chemical to carry out the photocatalytic activity tests under UV light irradiation. It was observed that the trace metal ions doped TiO2 fibers with pure crystalline phase, anatase or TiO2(B), all displayed less photocatalytic activity than the non-doped fibers, and only the doped mixed phase fibers showed improved photocatalytic degradation activity (Figure 1). Obviously, the phase interface between anatase and TiO2(B) play an important role in enhancing the activity of the photocatalysts. We believe that the trace metal ions promote the separation of photogenerated charge carriers, and thus to improve its photoactivity, only when they exist in the phase interface. This study highlights new opportunities for the design and preparation of highly efficient photocatalysts.