With the progressive aging of the population, the long-term nursing care and drug safety for the elderly are gradually gaining attention. In Taiwan, nursing homes are the main institutes helping society or families take care of elderly people suffering from diseases. The aim of this study was to assess the prescribed medications of nursing home residents, the occurrence of DDIs and the association between the number of drugs and DDIs with a view to reinforce drug safety for the elderly. The findings of this study showed that the mean number of medications per resident was 5.74+/-2.4. Of the 323 samples, 81 (25.1%) had experienced DDIs, 63 (64.95%) were of moderate and 7 (7.2%) of major severity. The findings also showed that the number of potential DDIs increased as the number of medications used per residents increased. The residents with nine or more medications tended to have more DDIs, in comparison to those with one or two medications. The odds ratio (OR) was 11.389, which had reached statistical significance in difference. Therefore, to reduce potential DDIs, the number of medications for the senior people with chronic diseases should be properly controlled.