Behavioural finance challenges the traditional assumption that investors make fully rational decisions by highlighting the influence of psychological and emotional factors on financial behaviour. Despite the growing popularity of mutual funds in emerging economies, limited empirical evidence exists on how emotional biases shape retail investors' investment decisions. This study investigates the influence of four emotional biases—overconfidence, herding, loss aversion, and availability bias—on mutual fund investment decision-making among retail investors in Surat, India. A quantitative research design was adopted using a structured questionnaire administered to 202 mutual fund investors selected through convenience sampling. Data were analysed using descriptive statistics, Pearson correlation analysis, and multiple regression analysis in SPSS. The findings reveal that emotional biases are significantly associated with investment decision-making. Among the examined biases, overconfidence and loss aversion exert a statistically significant positive influence on investors' decisions, whereas herding and availability bias do not demonstrate significant effects when controlling for other behavioural factors. The regression model explains 57.5% of the variance in investment decision-making, indicating substantial explanatory power. These findings reinforce the growing relevance of behavioural finance in explaining investor behaviour beyond conventional rational choice models. The study contributes to the behavioural finance literature by providing empirical evidence from an emerging market context and offers practical implications for investors, mutual fund companies, financial advisors, and policymakers seeking to promote more informed and rational investment decisions through behavioural awareness and investor education.