In our previous work the nano-sized hydroxyapatite (nano-HAP) with uniform morphology has been firstly synthesized by a wet chemical method based on dialysis, but the dialysis efficiency was not investigated in detail. In this paper, the removal efficiency of impurity ions such as NH4 + and NO3 - was respectively evaluated by calculating the concentration of the representative irons between the inner slurry and outer distilled water. Results showed that 99% NO3 - ions and 96.9% NH4 + - ions in the slurry has been eliminated. In the first dialysis time, the NH4 + ions diffuse faster than the NO3 - ions due to their smaller size. In the following dialysis times, the dialysis efficiency of NO3 - ions is higher than that of the NH4 + ions because of the presence of higher NO3 - ions concentration gradient. The final nano-HAP is also characterized by XRD, TEM, and FT-IR. It is revealed that the products are stick-like with a length of about 150nm and a diameter of about 20-50 nm. Current work suggests that dialysis is an efficient purified method for nano-HAP production and especially can be applied to industrial preparation of fine nano-sized HAP powders.