A sustained release dosage form comprising Quetiapine or a pharmaceutically acceptable salt, polymorphs, solvates, hydrates thereof and one or more non-gellable release controlling polymer and one or more pharmaceutically acceptable excipient(s). A sustained release dosage form comprising first granulation comprising Quetiapine or its pharmaceutically acceptable salts, polymorphs, solvates, hydrates thereof and one or more release controlling material; and second granulation comprising one or more release controlling material which is the same or different than the one or more release controlling material of the first granulation and optionally quetiapine or its pharmaceutically acceptable salts, polymorphs, solvates, hydrates thereof. A method of preparing the sustained release dosage form by first and second granulation followed by milling; blending the said milled granules after second granulation with lubricant followed by compression to form a sustained release dosage form. A sustained release dosage form comprising immediate release core comprising Quetiapine or a pharmaceutically acceptable salt, polymorphs, solvates, hydrates thereof and one or more pharmaceutically acceptable excipients; and sustained release coating comprising one or more non-gellable release controlling material.