Purpose - The purpose of this paper is to investigate the potential benefits or detriments of team management on fund performance in the mutual fund market. An additional purpose of this study is to examine the optimal number of managers in a fund industry for superior performance. Research design, data, and methodology - This paper investigates the effect of managerial structure on fund performance in the Korean active mutual fund market between 2001 and 2008. For this, we analyze two risk-adjusted performances measures- the capital asset pricing model (CAPM) and the three-factor model of Fama & French (1993). Results - First, we found that single-managed funds exhibited superior performance. Second major finding was that as the number of managers in a fund increases, the fund performance deteriorates. Finally, the results reveal that the sharpest performance drop occurs when team size increases from a 5-person team to a 6-person team. Conclusions – The results suggest that the management structure can be a source of competitive advantage for fund performance. As considering fund performance is the outcome of managers’ decision-making, this study contributes to not only the financial literature but also the literature in other areas, such as management and general business.