The present invention relates to a stable formulation particularly suitable for the anti-mesothelin immunoconjugate MF-T-SPDB-DM4. The described stable aqueous formulation comprising MF-T-SPDB-DM4 is directly suitable for therapeutic applications and for subsequent lyophilization. The lyophilized powder can be reconstituted with water to create a reconstituted solution which is again suitable for therapeutic applications. It is a further object to provide a stable reconstituted protein formulation which is suitable for therapeutic administrations.
