Real-time monitoring of liquid's viscosity has significant meaning in many areas. To adjust the viscosity, glycerol solutions with various concentrations have been widely used. Different types of viscosity sensors have been developed using various principles. However, these sensors have complicated fabrication and testing procedures and are not truly compatible with fluidic systems for on-site viscosity detection. Sensors based on single-walled carbon nanotubes (SWNTs) have attracted significant attention in recent years due to their smaller size, more uniform geometry, and more consistent performance. In this paper, we report a novel lab-on-a-chip device with integrated SWNT nanosensors for glycerol concentration detection, which is an indirect indication of fluid's viscosity. The device enables real-time, in-channel measurements of the concentration of flowing aqueous glycerol solutions. The experimental results show that our device has a relatively high sensitivity for glycerol solutions. The sensor resistance increases when the glycerol weight ratio rises, indicating an increased viscosity. The sensor also responds to the flow velocity when the glycerol weight ratio is kept at a constant level. Our results demonstrate a simple and effective approach to create nanoscale in-channel glycerol sensors. The knowledge obtained from this research can enable the development of future novel glycerol-based viscosity sensors for biomedical applications.