Background: Chinese women's age at first marriage increased for more than three years on average during the short period between 1970 and 1979. Demographers attributed it to the 'later, longer, fewer' family planning policy of the 1970s whereas some sociologists suggested that the 'send-down' movement in 1968-1978, which mobilized over 17 million urban youths and sent them to the countryside, may also have played a role. Methods: Using newly available high-quality national representative sample survey data, we estimated the effect of being sent-down on women's age at first marriage. We then conducted counterfactual simulations to decompose the total increase in women's age of marriage between 1970 and 1979 into a component attributed to the send-down and a residual component attributed to other factors. Results: Our results suggest that being sent-down delayed Chinese women's age at first marriage by 1.2 years. For urban women, this accounts for 13.3 percent of the total increase in their age at first marriage between 1970 and 1979. For urban and rural women together, the overall contribution of send-down to the increase in their age of marriage is less than one percent. Conclusions: On one hand, the send-down policy did not play an important role in the demographic transition process in China. On the other hand, for the 17 million sent-down youths, being forced to leave home and settle in a harsh and unfamiliar rural environment at very young ages marked a hard transition to adulthood and inevitably disrupted their normal life course. Delayed marriage, as revealed by this study, may be just tip of the iceberg.