本文的目的是分析夜間活動對台灣民眾的社會行為與主觀福祉的影響。根據Melbin（1978）及傅仰止（1997）的研究，夜晚是社會生活的一個前沿，這個新擴展的時空領域激發個人的非慣俗傾向。本文延伸了夜晚疆界的論點，提出數個可能的影響範疇，就晚睡與夜晚在外對放鬆自己（菸酒消費、看電視與上網）、社會網絡與主觀福祉的潛在影響進行評估。利用「台灣社會變遷基本調查」四波的跨年資料（1995、2000、2005及2010年），我們的迴歸分析結果顯示，夜間活動人口的基本特徵是都會中較年青的族群。同時，服務業工作者在夜間活動的頻率頗高，反映了這個部門在夜間擴張的傾向。夜間活動與非慣俗性的相關並不高，這點不支持傅仰止的觀點，但與消費菸酒、接觸陌生人的相關較高。我們的結論是，夜晚疆界仍然存在，但白天與夜晚區隔出來的並非是驚世駭俗的想法，而是煙酒消費和較開闊的人際網絡。

This study aims to investigate the influence of nighttime on social behaviors and attitudes among Taiwanese people. Melbin's (1978) idea of ＂night as a frontier＂ suggests that night constitutes a unique social space which encourages unconventional values and deeds (Fu, 1997). We further extend the theorizing of frontier and propose several hypotheses for empirical testing, with a new attention to the effect on slackening and social relationships. Pooling four waves of data from the Taiwan Social Change Survey (1995, 2000, 2005 and 2010), we replicated previous findings that urban youth is a major group of ＂night owls＂. We additionally show that people working in the service sector more likely are awake and being outside home after midnight. However, these night owls are not more unconventional in values, a finding differing from Fu's (1997) study of Taiwan sample. Night activities yet correlate with consumption of tobacco and alcohol and contacting with unknown persons. We conclude that while nighttime remains be a frontier, what divides day people and night owls is not freaky thoughts but use of psychoactive substances as well as widespread personal relationships.