The study examined the relationship between adoption of online tax systems and financial performance of small-scale enterprises (SSEs) in Wakiso District, Uganda. A descriptive cross-sectional research design was adopted to assess how online tax systems including e-registration, e-filing, e-payment, and digital tax compliance affect financial performance. The target population comprised registered SSEs in Wakiso District, with a sample size of 371 respondents determined using Krejcie and Morgan’s (1970) sample size table. A total of 350 valid responses were obtained, representing a response rate of 94.3%. Descriptive statistics including means, standard deviations, frequencies, and percentages were generated to summarize respondents’ characteristics and key variables. Regression analysis further showed that adoption of online tax systems significantly predicts financial performance, with a regression coefficient of β = 0.690 (p = 0.000), indicating that a one-unit increase in adoption leads to a 0.690-unit improvement in financial performance. The coefficient of determination (R² = 0.546) suggests that 54.6% of the variation in financial performance is explained by adoption of online tax systems. The study concludes that effective adoption of online tax systems enhances profitability, efficiency, and financial stability of SSEs and recommends improving system usability, technical support, and taxpayer education.