Thubana seimaensis is a moth in the Lecithoceridae family. It was described by Park in 2013. It is found in Cambodia. The wingspan is 15.5-16 mm. The forewings are uniform pale greyish fuscous throughout, with a dark-brown basal fascia. There is a pair of stigmata presented: the smaller one at the middle and the larger blackish one at the end of the cell.