This paper investigates the effect of equity valuation on external financing of firms listed on Korea stock exchange over the period 2000-2016. To do so, I use the methodology of Rhodes–Kropf et al. (2005), which breaks down the market to book ratio (M/B) into three components; long-run value to book (LVTB), firm specific error (FSE) and time-series sector error (TSE). I find that both long-run growth opportunities (LVTB) and two misvaluation factors (FSE and TSE) have a significantly positive effect on stock issuance, but not on debt issuance, implying that managers make decisions to implement a seasoned equity offering (SEO) when the firm has a long-term growth opportunity, or when the equity or the industry is overvalued. Managers often issue stocks for long-term growth opportunities to meet their investment needs (or to repay their debt obligations), while strategically issue stocks at the time their company or their industry is hot.