This study was to analyse the degeneration of the Retinal Nerve Fiber Layer (RNFL) and optic disc and the relationship between optic nerve damage and the severity of cognitive impairment in patients with Alzheimer’s disease (AD) and Mild Cognitive Impairment (MCI). The RNFL thickness and optic disc variables were assessed by optical coherence tomography in patients with MCI and AD and control subjects. Moreover, the correlation coefficients among RNFL thickness, optic disc parameters, and Mini- Mental State Examination (MMSE) scores were investigated in AD and MCI patients. RNFL thickness was significantly thicker in control group than that in the other two groups (P<0.05). The significant difference was detected between groups AD and MCI (P<0.05). Cup-to-disc ratio and pallor area-to-disc area ratio were increased but disc rim area was reduced in groups MCI and AD compared with in normal group (P<0.05). The significant difference was existed between groups AD and MCI (P<0.05). Pearson’s correlation test showed that compared with MMSE scores there was negative correlations in cup-to-disc ratio (P<0.05) and pallor-to-disc area ratio (P<0.01), but positive correlations in total RNFL thickness (P<0.01) and disc rim area (P<0.01). These results indicated that there was the degeneration of RNFL in MCI and AD patients. Moreover, the correlations among RNFL thickness, optic disc parameters and MMSE scores revealed that the severity of the optic nerve damage was increased along with the aggravation of the disease.