"If it were used correctly, it could be of real benefit, but unfortunately it's exploited for trivial matters," Sheikh Abdul Aziz al-Sheikh said on his "Fatwa" television show broadcast late yesterday.
Twitter is "the source of all evil and devastation", the mufti said.
"People are rushing to it thinking it's a source of credible information but it's a source of lies and falsehood."
Saudi Arabia adopts a strict version of Sunni Islam, including a segregation of the sexes, that influences all aspects of life in the Gulf kingdom.