Root storability of 'Beniaka' and 'Beniazuma' sweet potatoes was investigated as related to root composition and plant growth before harvest. Percentage of marketable roots after storage of 6 months at 13 °C was high in the roots which contained proteins at 0.4 g•100 g^-1FW and higher in 'Beniaka', and at 0.8 g•100 g^-1FW and higher in 'Beniazuma' at harvest. Percentage of marketable roots after storage was also related to the fresh weight of plant tops (tFW•ha^-1) and N content of whole plants (kg•ha^-1) at harvest. However it didn't show significant relationship with skin color and starch content. Plants with top/root (T/R) ratios of 0.8 to 1.3 at harvest produced roots of high storability and good quality in the two cultivars. These results indicate that root protein contents and T/R ratios could be useful guides for judging the storability of harvested sweet potato roots.