本研究探討造成當前生育率下降的原因。過去半世紀，多數國家的生育率呈現不斷下降的情形。早期生育率的下降可以歸因於工業化下社會轉型的結果，主要因素為女性的教育程度、薪資與勞動參與率等。然而二十世紀末期，許多已開發國家的女性相關社會經濟特徵皆已發展趨緩，無法再用以解釋二十一世紀初生育率仍在下降的事實。因此我們認為造成近十年來生育率下降的原因，應與已開發國家積極推動老年經濟保障政策使家庭財富流動方向改變有關。本研究以台灣家庭新生見生育個數為研究對象，採用台灣家庭收支調查資料1990年至2008年分析實施老年經濟保障政策對個人生育意顧的影響。我們利用卜瓦松迴歸模型進行估計，得到的結果顯示政府愈強化老年經濟安全將會愈加排擠個人的生育意願。本研究進一步估計實施老年經濟保障政策對家庭財富流動方向的影響估計結果說明老年經濟保障將導致家庭向上流動的財富減少、向下流動的財富增加此結果隱含老年經濟保障政策使養育成本相對提升，導致排擠生育意願。 This study investigates the effects of old-age economic security on fertility. The fertility rate has exhibited a downward tendency in many countries following the postwar baby boom. In the early years the fertility rate decreased due to industrialization. While various factors, such as the female education years, wage and labor participation rate, had all developed by the end of the 20th century, they have been unable to explain the current fertility rate tendency. We consider that the old-age economic security causes family wealth flows to veer around, which in turn reduces the desire for fertility. In this research we use multi-year cross-sectional data from the Survey of Family Income and Expenditure since 1990 to 2008 to investigate the old-age economic security effects. The standard Poisson and zero-inflated Poisson estimations are adopted to address the effects on the number of births. By considering the endogeneity of the old-age economic security and fertility, our empirical results show that the stronger the old-age economic security is, the more the number of births is crowded out. We also estimate the effects of the old-age economic security on family wealth flows . It is found that the old-age economic security decreases the upward wealth and increases the downward wealth. This implies that the family bearing cost increased in relative terms and led to crowding out of the number of births.