Bismuth-doped tin dioxide (BTO) nanopowders were prepared by wet chemical co-precipitation method using tin tetrachloride (SnCl4) and bismuth nitrate (Bi(NO3)(3)) as raw materials. Effects of calcination temperature and post treatment methods on particle size and crystalline phase transition of bismuth tin precursor (BTP) were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric-differential scanning calorimetric instrument (TG-DSC) and X-ray photoelectron spectroscopy (XPS). The optimal calcination temperature of BTP was found to be about 873 K. A novel post treatment process with polyacrylamide (PAM) in the preparation of nanometerials was presented for the first time. Experimental results showed that nonionic PAM is a highly effective additive, which not only speeds up the filtration of precursor, but also effectively reduces the formation of hard agglomerates. The average size of BTO nanopowders prepared using nonionic PAM as a filtration aid and disperser is smaller than 10 nm. We believe this post treatment method will come into wide use for preparation of many nanosized materials.