A facile, green and versatile method has been developed to prepare MoSe2 nanodots through polyvinylpyrrolidone (PVP)-assisted liquid phase exfoliation. The obtained nanodots showed a narrow size and thickness distribution. Moreover, these ultrasmall MoSe2-PVP nanocomposites could serve as efficient light-absorbing agent for photothermal therapy with negligible cell toxicity and appreciable photothermal effect.