1949年以後眾多神父修女來台傳播福音，加上大批外省人湧入，天主教快速成長，但60年代初期到中期，改信天主教的人數成長趨緩，此後更急遽下降。對此現象的常見解釋，認為台灣經濟發展與都市化造成的物質主義與消費主義使民眾遠離宗教。但本文利用台灣天主教瑪利諾會台中與苗栗兩個牧區的史料，論證台灣天主教會的沒落，來自其政治、經濟與道德影響力衰退等複雜因素。50年代末，美國已無意幫助台灣反攻大陸，60年代中期後投入越戰使國內情勢不穩，在亞洲的地緣政治勢力受限而對台支援能力衰退，這些都削弱了天主教會的家長式作風。60年代中期後天主教會的衰頹不是由於台灣民眾的物質主義興起，而是他們對美國救援物資的依賴程度降低。第二屆梵諦岡大公會議引發許多神職人員彼此之間，以及他們和平信徒間的爭端；加上教會在工業化社會中尚在尋找本身定位，以及社會加速走向世俗化和去宗教化，這都導致教會所具有的道德與精神上的權威、如慈父般的堅強救贖者形象，愈加模糊。都市化過程中離鄉的天主教徒喪失原有的社群網絡，不易融入都市堂區，而本省人或原住民更難加入說國語的外省人為主的都市堂區。70年代末之後台灣國族意識興起，主教和華籍神職人員對本省人的傳教工作並沒有進展，使天主教在台灣社會的發展更加困難。

The Catholic Church in Taiwan had a rapid growth since 1949 after the large influx of missionaries and Mainlanders from China. In the early to mid-1960s, the rate of conversions began to slow, then decreased steeply. Many believe that materialism and consumerism resulted from Taiwan’s economic growth and urbanization had pulled people away from the Church. By analyzing the documents of two Maryknoll missionary regions, the diocese of Taichung and the deanery of Miaoli, I argue that the falling off of Church membership was due to a complicated set of causes, including the Church’s decreasing political, economic, and moral power. By the end of 1950s, US had been unwilling to back KMT’s recovery of China. In the mid-1960s, US’s engagement in Vietnam and domestic turmoil limited its geo-political power in Asia and its capacity to support Taiwan. All these led to the weakening of the Church’s political power. Also the decrease in dependency of the Taiwanese on US relief goods reduced the Church’s economic power. The Second Vatican Council generated controversy among many clergy and laity and the image of the Church as an authoritative but benevolent Father lost its old clarity. In the process of urbanization, many Taiwanese and aboriginal Catholics who migrated to the cities were excluded by the Mainlander-dominated urban parishes. With the rise of Taiwanese national consciousness in the late 1970s, the bishops and Chinese clergy’s firm stand on the side of the KMT constituted a further obstacle to the flourishing of the Catholic Church among the Taiwanese.