Microfluidic systems with modular components are attractive alternatives to monolithically integrated microfluidic systems because of their flexibility. In this study, we apply the modular concept on a water-head-pressure-driven microfluidic oscillator and obtain a widely tunable flow rate and fluidic switching period. Modular fluidic resistors can be easily mounted onto and demounted from a main chip by means of plastic male connectors. The connectors enable a leak-free connection between the modular resistors and main chip (leakage pressure > 140 kPa). With modular resistors, we show independent control of the flow rate and flow switching period of the oscillator system in a wide range (2.5 s-6.4 h and 2 mu L/min-2 mL/min). This modular approach can be used to enhance the flexibility of instruction-embedded microfluidic circuits in which their operational range is limited.