The development of microfluidics technology offers new possibilities for investigating the unique behavior of complex fluids. In this talk, the dynamics of filament thinning and drop breakup of complex fluids, such as dilute polymeric and micellar solutions, is investigated in a cross flow microfluidic device. Qualitatively, both polymeric and micellar fluid filaments show much slower evolution, and their morphology features multiple connected drops. Micellar solutions may show fracture dynamics, which depends on the continuous phase viscous stresses (i.e. flow rate). The filament thinning process is quantified by the decrease in filament diameter h(t) as a function of time. Results show that the thinning process of both dilute polymeric and micellar solutions consists of two exponential regimes, while the Newtonian fluid shows a single exponential regime. An algebraic decay is observed for all fluids near the filament breakup. We show that the exponential flow thinning behavior allows a measurement of the extensional viscosities of both Newtonian and complex fluids.