Abstract: Background: In present study, scolicidal effect of CM11 peptide against protoscolices of hydatid cyst was investigated. Materials and methods: The liver hydatid cysts were collected from the slaughtered sheep in the Mashhad abattoir in the summer of 1397. Echinococcus granulosus protoscolices were collected and washed three times with 0.9% normal saline. At first, the percentage of viability of protoscolices was evaluated using Eosin staining. Different concentrations of CM11 peptide (16, 64, 128, and 256 μmol.), along with positive control (Savlon) and negative control group (o.9% normal saline), were used against protoscolices (viability of 90%) for 30, 60, 120 and 240 minutes at a 37°C incubator. Eosin staining was done at the end of the incubation time, and the images were taken with a camera equipped with Tcapture software. Finally, the number of dead and live protoscolices was determined by ImageJ software, and the viability and mortality percent was calculated. All the tests were performed five times. Data analysis was carried out by using sigma stat (version 3.5). P value 0.05 was considered statistically significant. Results: Up to 2 hours, the effect of all concentrations of CM11 peptide on protoscolices was not significant compared to the negative control group. However, after 4 hours of exposure, 128 and 256 μm of peptide, were significantly decreased the viability of protoscolices (p 0.05). Conclusion: With regard to the results of this study and considering the resistance of the present antiprotoscolics drugs, the CM11 can be used as a relatively effective peptide against protoscolices in future research. Obviously, it is crucial to improve the effective dose and time of this peptide. Concomitant use of this peptide with other effective compounds on protoscolices and structural changes in the peptide will potentially reduce the effective dose and time of action. Keywords: CM11, Hydatid cyst, Invito assay

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