organic light-emitting diodes (oLeDs) using a liquid organic semiconductor (LoS) are expected to provide extremely flexible displays. Recently, microfluidic OLEDs were developed to integrate and control a LOS in a device combined with microfluidic technology. However, LOS-based OLEDs show poor-colour-purity light emissions owing to their wide full width at half maximum (FWHM). Here we report liquid/solution-based microfluidic quantum dots light-emitting diodes (QLEDs) for highcolour-purity light emission. Microfluidic QLEDs contain liquid materials of LOS for a backlight and QDs solutions as luminophores. The microfluidic QLED exhibits red, green, and blue light emissions and achieves the highest light colour purity ever reported among LoS-based devices for green and red lights with narrow FWHMs of 26.2 nm and 25.0 nm, respectively. Additionally, the effect of the channel depth for the luminophore on the peak wavelength and FWHM is revealed. The developed device extends the capabilities of flexible microfluidic OLEDs-based and QDs-based displays. Organic light-emitting diodes (OLEDs), composed of organic semiconductors, have been applied in various devices as displays owning to their superior features than liquid crystal displays such as wide view angle, light weight, flexibility, and short response time 1-3. Recently, solvent-free organic liquids were reported 4-7. These are π-conjugated moieties with bulky and flexible side chains, which lower the melting point of the molecules, so they adopt a liquid state without any solvents at room temperature. Although characteristics of devices using such liquid materials are inferior than that of devices using solid materials, the use of liquid materials prevents detachment between the liquid layer and electrodes even if device shape changes. In addition, conventional solid type-organic semiconductors are more flexible compared with inorganic counterparts. However, they show poor resistance under large deformation such as stretching and bending due to their inherent rigidity and highly ordered structures 8. On the other hand, solvent-free organic liquids have not any limitation in flexibility because they are fluidic materials. Consequently, the solvent-free organic liquids are expected to realize truly flexible devices. D. Xu and C. Adachi developed liquid OLEDs using a solvent-free organic liquid named a liquid organic semiconductor (LOS) as an emitting layer 9. An LOS shows strong charge transfer and fluidity in the neat state 10. Moreover, liquid OLEDs are able to overcome the short lifetime of solid OLEDs by replacing the degraded LOS with a fresh sample 9,11. In 2013, we applied microfluidic technology to the liquid OLEDs to integrate the LOS on a chip, and coined the term microfluidic OLEDs 12-16. Microfluidic OLEDs show various functionalities using the liquid features of LOS such as high flexibility 13 , on-demand colour tunability 14 , and emission recoverability 14. However, liquid OLEDs show a wide full width at half maximum (FWHM) of 70-100 nm, as do convent...