Against the backdrop of potential irrational trading behaviours in financial markets, this study investigates the V-shaped disposition effect in the selling activities of portfolios managed by securities investment funds in China. Utilising quarterly holdings data (2018–2024) of Chinese securities investment funds, alongside daily turnover rates and closing prices of their fund-heavy stocks listed in China's A-share market, a Fama-MacBeth regression analysis is conducted. The empirical results provide robust evidence of a significant V-shaped disposition effect in these fund investments, primarily driven by speculative trading. Moreover, this effect significantly and positively predicts future stock returns of Chinese A-shares. This study enhances understanding of institutional investors' trading behaviours—particularly mutual funds in China—and their decision-making processes in financial markets.