In the past decade, US middle-market private equity has experienced an increase in fundraising and buyout activities. At the same time, many mega-fund managers have gradually entered the middle market, hoping to create value by focusing on operational improvement in middle-market companies. The entrance of mega-fund managers into the middle market likely has had an impact on middle-market fund managers, who are the biggest players in the middle market. Given the limited existing literature on middle-market private equity, this research intends to fill in the gaps by analyzing the association between increasing mega-fund managers’ interest in the middle market and middle-market fund managers’ investment opportunities. The results will provide guidance for middle-market fund managers and mega-fund managers to make strategic decisions in the middle market. To analyze data from Preqin, I used Wilcoxon/ Kruskal-Wallis Test and Median Test to measure whether there is a statistically significant difference in mega-fund managers’ share of the middle market before and after 2008. This research concludes that mega-fund managers’ expansion in the middle market, especially in the lower middle market and core middle market, is associated with fewer deal opportunities for middle-market managers during the past decade.