Although its importance as an economic basis of the 'Ulama's power has been repeatedly pointed out. the institution of VAQF (plu. OWQAF, pious endowment) in Twelver Imami Shi'i tradition is probably one of the issues on which no serious and concrete investigation has ever been made. This may be partly because of paucity of documents concerning VAQF and partly because the people involved in VAQF administration did not want its actual proceedings to be made disclosed. In this paper, the author makes an attempt to comprehend the meaning of VAQF from two different but complementary aspects; its legal theory in Twelver Imami Shi'ism presented by various legal scholars such as 'Allama Hilli and Khomeini and so forth, on the one hand and the case study of VAQF administration around the city of Qom and its neighboring areas by utilizing several ketabchehs written in the latter half of the 19th century on the other. Through this analysis, though far from reaching any general conclusion, the following remarks could be made: the legal theory of VAQF, which in many ways was followed, was not always observed as it is presented by the FOQAHA, and several influential figures took advantage of the institution for their personal profit. This being the case, however, the city of Qom, which has been one of the most important religious centers in Iran with its religious architecture and institutions, had been greatly enriched and strengthened by the income from pious endowment, thus enabling the 'Ulama to enjoy their power directly or indirectly backed by this economic prosperity.