The starch content of Japanese sweetpotato [Ipomoea batatas (L.)] cultivars is rated among the highest in the world and has been accomplished via a national breeding programme conducted for more than 50 years. The first step of the programme was to accumulate genes for high starch content in local cultivars whose starch content ranged from 14 to 20%. A starch content of 15-20% with higher storage root yield was obtained from the offsprings. Genes from foreign cultivars were then transferred to the local cultivars. Cultivar ‘Koganesengan’ was developed from this cross producing a starch content of 22-26% and considered to be a high storage yield cultivar. Wild relatives were also used to increase genetic variation, and ‘K123’ (19% starch content but no storage root) a hexaploid wild plant was crossed with cultivated sweetpotato. The resulting hybrids were used to backcross (BC) with improved cultivars. From the resulting BC2 progenies, ‘Minaniyutaka’ was selected and released which had a lower starch content (19-22%) but produced more storage roots than ‘Koganesengan’. Recently, ‘Hi-starch’ and ‘Satsuma-starch’ were released. Both had the highest level of starch content (28-30%) among the cultivars released in Japan.