Mini warehouses have become an increasingly popular storage solution in densely populated metropolitan areas. By the end of 2023, the industry had established 827 sites across Taiwan, with 709 located in the six main cities, accounting for 85.7% of the total nationwide. However, the presence of unknown stored contents in high-density environments raises significant fire safety concerns. Without proper regulations, fires in mini warehouses can rapidly escalate and pose severe risks to surrounding communities. This study aims to explore the fire behavior of mini warehouses under different conditions where a total of four full-scale experiments and two computer simulations were conducted. Results show that keeping the warehouse door closed is a critical factor in controlling fire spread, due to its effect on airflow and oxygen supply. Additionally, mini warehouses featuring wooden mezzanines demonstrated greater fire hazards owing to the added combustible load. Simulation outcomes closely matched the experimental data in terms of fire growth rate and peak temperatures, supporting the validity of the model. Overall, the findings highlight the high fire risk associated with current mini warehouse setups and emphasize the urgent need for targeted fire safety regulations. This research serves as a warning and a reference point for future policy development and risk management in urban storage facilities.