Recently, a new muscular disorder has been reported in chicken M. pectoralis major called Wooden Breast that might be linked to intensive growth selection. The purpose of this study was to find the influence of Wooden Breast condition on protein composition of the breast muscle with special emphasis on myofibrillar and sarcoplasmic protein fractions. For fulfilling the aims of the study, a total number of 34 pectoralis major muscles from both Wooden Breast and normal chickens (Ross 508, Aviagen Ltd, Scotland) were used to evaluate protein composition, protein profile of sarcoplasmic and myofibrillar proteins and their changes, by doing one-dimensional SDS-PAGE analysis. M. Pectoralis major defected by Wooden Breast demonstrated significant decline in sarcoplasmic (P?0.001) and myofibrillar (P?0.05) protein content, in comparison with normal breast muscles. Furthermore, gel electrophoresis indicated significant changes in the intensity of 18 sarcoplasmic protein bands and 7 myofibrillar protein bands. Majority of affected sarcoplasmic proteins were glycolytic enzymes. Moreover, impacted myofibrillar proteins play a role in muscle fibre integrity (e.g. desmin) or calcium signalling. Results of the present study also revealed desmin overexpression with coexistence of a desmin fragment in Wooden Breast which was confirmed by Western-blot technique. In conclusion, the findings of this study indicated defected chicken breast with Wooden Breast contained less protein and the composition differed compared to normal chicken breast muscle, which proves the influence of Wooden Breast condition on protein characteristics of chicken breast muscle. Further studies are needed to interpret the protein changes in the Wooden Breast and the possible role of these changes on metabolic and structural status of the muscle.