The present invention relates to various polymorphic forms of lomitapide or its salts and processes for preparation thereof. The present invention provides Lomitapide mesylate in solid amorphous form and process for preparation thereof. The invention also provides an amorphous solid dispersion of lomitapide mesylate. Further, various crystalline forms of lomitapide mesylate like A, B and C and process for preparation thereof are provided. The invention also provides crystalline forms of lomitapide free base, in particular Form I and Form-II and their preparation. The invention further provides compositions comprising various forms of lomitapide and its salts.
