Since the nonprofit organizations (NPOs) have been increasingly well-built within the last decade, their public-spirited services providing is somehow unable to the replaced by the government and enterprise, having become solemnly the third sector organization. As to the inefficiency of NPOs would give rise to a low quality in public services and a waste in social resources, this study aims at assessing the efficiency of social welfare charitable foundations of Taiwan in the year of 1992. This study adopts CCR and BCC model of Data Envelopment Analysis to measure aggregate efficiency, pure technical efficiency and scale efficiency of the charitable foundations. This study further divides the charitable foundations into three sub-groups in terms of character of main donors and derives a difference analysis from an efficiency comparison among those. Finally, from implementing Slack Variable Analysis, the suggestions to direct charitable foundations to efficiency improvement are drawing. The results showed that the efficiency of charitable foundations in Taiwan is generally low. Among them, the foundation that the public supports is averagely the most efficient, the foundation that private supports has the lowest average efficiency. In addition, this study also found that the aggregate inefficiency of the charitable foundations mainly comes from pure technical inefficiency rather than scale efficiency. Therefore, taking pure technical inefficiency into a detailed consideration, the evidences generating from Slack Variable Analysis illustrated that a reduction in the amount of funds among input items and an increase in contributing expenditures among output items are leading activities for relatively inefficient charitable foundations.