線上社交平台是敏感性社會議題常見的討論場域，如何提升個人意見表達或參與社會議題的意願，將是促進公民參與及國家發展的重要因素。本研究結合沉默螺旋理論與社會資本理論，探討個人在線上社交圈中面對敏感性社會議題時的意見表達意願，並以探索性研究角度，探討社會資本理論在其中的調節影響。研究結果發現：(1)個人感知的意見氣候一致性會正向影響個人的意見表達意願；(2)個人的害怕孤立感與自我呈現疑慮皆會負向影響個人的意見表達意願（然後者的影響在同婚議題中並不顯著）；(3)對新興與過渡型議題而言，社會資本負向調節自我呈現疑慮對意見表達意願的負向影響；(4)社會資本在感知意見氣候一致性及害怕孤立感對意見表達意願之影響的調節效果未獲支持。

Online social platforms are common field for discussing sensitive social issues. How to strengthen personal intentions for opinion expression or participation in discussions is key to civic engagement and nation development. This research integrates the spiral of silence and social capital theories to investigate the issue of opinion expression for sensitive social issues. Also, this research also explores the moderating effects of social capital on the main effects. Results show that (1) consistency of perceived climate of opinion positively affects intention for opinion expression, (2) fear of isolation and self-presentational concern negatively affects intention for opinion expression (the influence of the latter, however, was insignificant for same-sex marriage issues), (3) for emerging and transitory opinion types, social capital negatively moderates the negative relationship between self-presentational concern and intention for opinion expression, and (4) the moderating effect of social capital on the influences of either consistency of perceived climate of opinion or fear of isolation on intention for opinion expression failed to be supported.