The aim was to investigate the neural basis of visual attention deficits in Alzheimer's disease (AD) patients using functional MRI. Thirteen AD patients and 13 age-matched controls participated in the experiment of two visual search tasks, one was a pop-out task, the other was a conjunction task. The fMRI data were collected on a 1-5T MRI system and analyzed by SPM99. Both groups revealed almost the same networks engaged in both tasks, including the superior parietal lobule (SPL), frontal and occipito-temporal cortical regions (OTC), primary visual cortex and some subcortical structures. AD patients have a particular impairment in the conjunction task. The most pronounced differences were more activity in the SPL in controls and more activity in the OTC in AD patients. These results imply that the mechanisms controlling spatial shifts of attention axe impaired in AD patients.