Persistent variations between statutory tax rates and actual taxes paid by banks in Nigeria have raised concerns about increasing tax aggressiveness and its implications for government revenue. This study examines the determinants of tax aggressiveness among quoted deposit money banks in Nigeria, focusing on the effects of liquidity, firm size, and profitability on effective tax rate (ETR). The study adopts an ex-post facto research design and utilizes panel data obtained from the annual reports of ten listed banks over the period 2012–2024. Data were analysed using descriptive statistics, correlation analysis, and panel regression techniques, including the random effects model. The findings reveal that liquidity), firm size, and profitability have negative and statistically significant effects on ETR, indicating that more liquid, larger, and more profitable banks tend to engage in higher levels of tax aggressiveness. The results suggest that firm-specific characteristics play a significant role in shaping tax behaviour in the Nigerian banking sector. The study concludes that existing regulatory mechanisms may not be sufficiently robust to curb aggressive tax practices among financially strong banks. The study recommends the adoption of risk-based tax audits, enhanced tax transparency requirements, and stronger regulatory collaboration to improve tax compliance. These findings contribute to the literature on corporate taxation by providing sector-specific evidence from an emerging economy and offer practical insights for policymakers and regulators.