en تخصصي Special پژوهشي Research <strong>Background:</strong> Cadmium is one of the heavy metals with harmful effects on different body organs and systems. The aim of this study was to investigate the harmful effects of cadmium, as a heavy metal, on the histological structure of bone and the expression of osteocalcin gene.<br> <strong>Methods:</strong> Forty chickens were obtained, anesthetized and their femurs were surgically removed. The real time polymerase chain reaction (PCR) was used to study the osteocalcin gene expression.<br> <strong>Results:</strong> The osteocalcin gene expression rate were: 1.000<span dir="RTL">&plusmn;</span> 0.1; 0.86<span dir="RTL">&plusmn;</span> 0.01; 0.63<span dir="RTL">&plusmn;</span> 0.09, and<br> 0.41<span dir="RTL">&plusmn;</span> 0.06 in the controls, experiment I, experiment II and experiment III groups, respectively (P < 0.05). Also, the nuclear pyknosis in osteocytes and decreased bone formation were observed in the histology slides of the chicken bones.<br> <strong>Conclusions:</strong> We conclude that cadmium adversely affected the chicken bones as evident by the decreased osteocalcin gene expression and the adverse effects on the bone histology.&nbsp; We recommend that plans be developed to prevent the outbreak of cadmium and other heavy metals in animal and human environment. Bone Formation, Cadmium, Gene Expression, Osteoblast and Osteocyte, Osteocalcin Gene 1 4 http://ijt.arakmu.ac.ir/browse.php?a_code=A-10-540-3&slc_lang=en&sid=1 Zahra Ahmadi 100319475328460011357 100319475328460011357 No Department of Basic Science, Faculty of Veterinary Medicine, University of Shushtar. Khoozestan, Iran. Milad Ashrafizadeh abriz, Iran. *Corresponding Author: Milad Ashrafizadeh, E-mail: dvm.milad73@yahoo.com 100319475328460011358 100319475328460011358 Yes Department of Basic Science, Faculty of Veterinary Medicine, University of Tabriz. Tabriz, Iran.