Dendrite arm spacings of alum inium and Al-Mn, Al-Cu, Al-Li,etc.14 aluminium alloys with minor Rare Elements added have been studied. Present investigation indicates that minor addition of Rare Earth Elements La,Ce or Yobviously refined the dendrite structure of commercial pure aluminium and aluminium alloys.The refining effect of Rare Earth Elements on dendrite arm spacings was directly related to the"quality"and'quantity'of alloying elements in the base alloy,this was reflected by the solute transportation characteristic parameter Po proposed in this paper;The refining effect of Rare Earth Elements on dendrite arm spacings was also related to the cooling rate during solidification. The higher the cooling rate,the weaker the refining effect of Rare Earth Element on dendrite arm spacings.Although some additives were indicated to be very effective in refining grain size of aluminium alloys,their refining effect on dendrite arm spacings were found to be very weak.