The present invention relates to novel and stable salt forms of quetiapine, processes for preparation, pharmaceutical compositions, and method of treating thereof. More particularly, the present invention provides novel acid addition salts of quetiapine wherein the acid counter ion is provided by an acid selected from the group consisting of benzene sulfonic acid, dibenzoyl-L-(+)-tartaric acid and di-p-toluoyl-L-(+)-tartaric acid. The present invention also provides novel polymorphic forms of quetiapine salts selected from the group consisting of quetiapine hydrobromide, quetiapine sulfate, quetiapine nitrate and quetiapine citrate.
