The effect of elasticity of the polyethylene oxide (PEO)-glycerol solution on the dynamics of droplet formation in a microfluidic T-junction was investigated experimentally. Four flow regimes were observed including slug, dripping, beads-on-string and stratified flows. Droplet formation process involves three stages: expansion, squeezing and stretching stages. The expansion stage is shorter for the droplet formation of PEO-glycerol solution in comparison with a Newtonian fluid. In the squeezing stage, the decrease rate of the minimum width of the dispersed thread is not equal-proportional to the change of the flow rate of the continuous phase. In the stretching stage, the thread length at breakup increases firstly before decreasing with the flow rate of the continuous phase, while the maximum value is positively relative with the flow rate and elasticity of the dispersed phase. The droplet size increases with the elasticity of the dispersed phase. A modified scaling law of droplet size is proposed based on an elasticity number. The results reveal that the effect of the fluid elasticity on the droplet formation mechanism is more remarkable than the droplet size. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.