SnO２ nano-crystalline grains with sizes in the range of 4—80 nm ar e systematically investigated using Raman spectroscopy. Besides SnO２ fundam ental-fre quency modes, a few weak Raman modes and a very strong and broad photoluminescen ce peak at about 700 nm can be observed. Our results show that bulk properties o f nano-SnO２ diminish but the defect-, surface-, and size-related fea tures dis play as grain size decreases. A critical size that divides respective predominan ce is determined to be about 20 nm. Bulk spectra with spectroscopic line broaden ing and position shifting, a surface mode and interface mode around 571 cm －１and 351 cm－１, as well as the O-H vibration modes of the water mol ecu les in SnO２ nanograins are characteristics of Raman spectra of nano- SnO２ with grain size below 20 nm. They are related to the microstructure change of the nanograins, i.e. they reflect the change of grain size, surface, and the in teraction between nanograins.