Abstract: The establishment of an absolute time scale for human evolution is of great importance to anthropology and archaeology. Thus the possibiUty of dating fossilized vertebrate bones by uranium-series method is quite attractive^ as 1) fossil bones are frequently associated with paleolithic sites and 2) the time range immediately beyond the 14C limit which spans from 40 thousand years to about 300 thousand years still remains inaccessible to most radiometric techniques.
The uranium-series dating is based on the assumption that the post-mortem U-uptake by buried bones is relatively rapid and reaches some saturation level after a time much shorter than the age of bones. Thus the restoration of the equilibrium between U and its daughter nuclei is determined by the decay-growth process only. But this is not always valid. In many eases U migrates continuously in (or out) of the bone after fossili- zation. Thiis leads to the necessity to measure both 230Th age and 231Pa age Tor every sam- ple, and the concordance between these two ages will be the proof of the validity of the closed-system assumption.
α-spectrosecpie technique of 213Pa/255U activity ratio and 231Pa age measurement is described. The validity of this technique is tested on the RKM-5 fossil coral sample which has been wildly measured as an international cross-check sample by many ura- nium-series dating laboratories.

Key words: Uranium-series dating; Dating of paleolithic sites; North China