Mitochondrial cytopathies represent a heterogeneous group of multisystem disorder that preferentially affects the muscle and nervous systems. Mitochondrial respiratory chain enzyme complexes (MRC) defect can be the cause of many unexplained neurological disorders including epilepsy, cerebral palsy, delayed development and hypotonia. We retrospectively reviewed clinical and laboratory features of 16 patients who showed defects in MRC activity, confirmed by biochemical assay from spectrophotometry in muscles to characterize clinical and laboratory features for MRC defects and provide more precise diagnosis and effective treatments. In the patients with uncontrolled seizure activity, developmental regression, characteristic features of bilateral symmetric high signal intensity at deep nucleus and/or white matter in T2WI, the mitochondrial cytopathies should be added to the list of differential diagnoses. And lactate elevation in magnetic resonance spectroscopy (MRS) can be useful in the diagnosis of mitochondrial cytopathies.