A high-speed camera was utilized to observe the formation of the droplet in viscoelastic fluid in flow-focusing microchannel. The microchannel with a square section of 600 μm×600 μm was used in the experiment. Silicone oil and polyethylene oxide (PEO) solution (0.1%

0.3%

0.6%) with 0.3% surfactant sodium dodecyl sulfate (SDS) were used as dispersed and continuous phases

respectively. Three flow patterns were observed: slug flow

dripping flow and jetting flow. The transition lines for different flow patterns were obtained. The dynamics of breakup for slug droplets was studied. The effects of two-phase flow rates

capillary number and elasticity number of the continuous phase on the size of slug droplet were investigated experimentally. The results indicated that the size of slug droplet decreased with increasing flow rate

capillary number and elasticity number of the continuous phase

but it increased with increasing flow rate of the dispersed phase. The impact of the elasticity of the continuous phase on slug droplet size was relatively small. The correlations for predicting the size of slug droplet were proposed by taking the ratio of two-phase flow rates

and the capillary number and Reynolds number of the continuous phase into account. The prediction result agreed well with the experimental data.