Medial rectus muscle palsy without involvement of the third cranial nerve is uncommon. Two cases of isolated medial rectus muscle palsy were associated with blunt trauma and mucocele of the ethmoid sinus which were studied with computed tomography and MR imaging. Computerized tomography(CT) is necessary to comprehensive radiologic structures for exact localization and to early diagnosis and appropriate surgical approach. We report these two cases of isolated medial rectus muscle palsy associated with mucocele and fracture of the ethmoid sinus which were managed through the external ethmoidectomy.