Fluid flow patterns with a gel reaction in a circular flow pipe are investigated experimentally. Solutions of 10 mass% polyvinyl alcohol (PVA) and 3 mass% borax are used as the working fluids. The flow channel consists of a transparent main flow pipe and a transparent branch flow pipe that is connected vertically to the main flow pipe. The solution of 10 mass% PVA flows in the main flow pipe under steady-state conditions. The Reynolds number (Re-m) based on the mean velocity and the diameter of the main flow pipe is less than 30. The borax solution is colored with blue dye to visualize the flow patterns and is injected once only from the branch flow pipe. The experimental results show three distinct flow patterns, namely, capsule, capsule+stretched, and capsule+stretched+fingering flow. Re-m and the ratio of the volume flow rate (beta) are used to predict quantitatively the flow patterns with gel reaction. The results show that, in the region in which beta is less than unity, capsule flow forms and beta is the governing parameter. In the region in which beta is greater than unity, Re-m is dominant for determining the flow pattern with gel reaction.