In Ouran High School Host Club what did his mom die of?

Answer 1

If you are talking about Haruhi's mother, she apparently died because she was sick. Im not sure if they elaborate any further on this in the manga or the anime, sorry.

hope i helped out though :)

If you're talking about Tamakis mother, then she isn't dead. She lives in France because of the agreement he was forced to make with his Grandmother. As for the other males, the Twins mother is still alive and shows up periodically though out the manga. And it is never said who the mothers of Kyoya, Mori and Hunny are, but they are assumed to be alive.