It is known that the penetration resistance depends on the grain size of soils and that fines-containing sands have smaller SPT N values than clean sands. When correlating the SPT blow count and relative density of sandy soils, it is essential to offer a proper interpretation for these effects. This paper presents an empirical correlation between N and Dr that allows for the important effects of grain-size and fines content of soils, and is therefore applicable to various kinds of sandy soils, including clean sands, sands with fines and gravelly sands. The proposed correlation is based on data of high-quality undisturbed samples secured by means of the ground freezing technique and measured SPT resistance of natural sandy soil deposits in Japan.