As well as being asked to post about this by a number of people, I’ve also seen these two used incorrectly a number of times. I think negative versions of words do get people confused – and why not, when you have odd things like “flammable” and “inflammable” knocking around …
These two don’t mean the opposite of one another, but they do have distinct, separate and different meanings.
Uninterested means not interested. “I was uninterested in his plans for world domination”; “the cat remained uninterested in my new party dress”
Disinterested means impartial. I think this must be connected with the idea of “declaring an interest”; the disinterested person has no interest or investment in either side of an argument. “Amid all the disucssions, the chair remained a disinterested party, keeping order between the warring sides.”
If you aren’t keen on sitting on the fence and want to get involved, you could quite easily be uninterested in being disinterested …
You can find more troublesome pairs here.
LibroEditing proofreading, editing, transcription, localisation 
Jane
August 8, 2011 at 9:56 am
In one of my extended essays at university I wrote disinterested instead of uninterested the whole way through. Handed the essay in, and woke with a horrid start that night having realised what I’d done. Had to go and plead with my tutor the next day to give me the essay back so I could sort it out.
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Liz at Libro
August 8, 2011 at 9:58 am
At least you realised in time! Would you like to write a guest post on pony books for this blog, by the way?
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Chandra Dev
September 1, 2011 at 9:21 am
Hi
I generally used to write “not interested” instead of “Uninterested”. which one is the good practice to use ? could you tell me ?
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Liz at Libro
September 1, 2011 at 9:36 am
Hi Chandra,
“Not interested” is absolutely fine and removes any possible confusion!
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