Cecropin X is a short cationic peptide with a broad antibacterial and antitumor spectrum. Here, we report the production of a tumor necrosis factor (TNF alpha)-cecropin X fusion protein under the control of a temperature-inducible P-R promoter in the bacterial expression vector pRC. During fermentation, we studied and optimized essential parameters including the type of host cells, medium, timing of induction, post-induction time and dissolved oxygen level. Using the suitable conditions in the fermentation, up to 20% similar to 23% of the total cellular proteins is produced as the fusion protein, mostly in the form of inclusion bodies. After washing, on average about 5.27 g dried inclusion bodies could be collected from 1 L broth and the purity of inclusion bodies reached 80%. Cecropin X obtained by cleaving the fusion protein with cyanogen bromide showed remarkable tumorcidal activity against mouse Lewis lung carcinoma 3LL in vivo.