Disinterested 无私 has two meanings. The first and most widely accepted one is “impartial; 公正 unbiased 公正的 by personal interest or advantage” as in “A disinterested observer is the best judge of behavior.”

The second meaning is “not interested, 不感兴趣” as in “Having not followed Justin Bieber’s career, she was disinterested in the artist’s new release.”（但是这个用法有争议不被用）

Uninterested means “have or show no feeling of interest; indifferent 漠不关心的.” A student who dislikes reading plays might be uninterested in studying the complete works of William Shakespeare.