Heat transfer and pressure drop in a spiral square channel is examined experimentally and analytically. The spiral channel was fabricated on a copper plate. The cross-section of the channel is square with 1-mm sides. A copper cap plate was bolted tight to seal the channel. Water and four silicone oils (0.65, 1, 3, and 10 cSt) were used as the working fluid; thus, Prandtl numbers from 5 to 110 were examined. The experiments were done once with the fluids entering from the side of the spiral channel and exiting from the middle of the spiral channel, and once with the fluids entering from the middle and exiting from the side. Heat transfer behavior over a wide range of flow rates from laminar to turbulent has been examined. Heat transfer enhancement due to the spiral geometry was observed, and a slight difference was reported between the side and middle inlet condition. The dimensionless mean wall flux and the dimensionless thermal flow length were used to analyze the experimental data instead of Nusselt and Reynolds numbers. The spiral channel has been discretized so that a single Dean number can be assumed in each cell, and an existing correlation was applied to calculate the average Nusselt number. The model prediction is compared with the experimental points. Pressure drop tests have only been conducted with water as the working fluid.