Although the segregation of dry granular surface flow has been widely studied, cases where the air is completely replaced by a liquid still remain unexplored. In this study, we report on experiments performed to investigate the phenomena of particle segregation and flowing behavior in a rotating drum with liquids of different viscosities and different filling degrees. The experimental results indicate that the viscosity of the interstitial fluid has a significant effect on the granular flow in the slurry granular flow. The segregation index and angle of repose are shown to decrease with increased liquid viscosity. When the liquid viscosity is the same, the increase in filling degree causes the segregation index to increase, while the net rate of mixing seems to decrease. A new dimensionless flow variable is used to distinguish the flow regimes. We find that the flow regime changes from rolling regime to cascading regime when the dimensionless flow variable is below a critical value. Furthermore, the change of segregation index occurs during the transition of the granular flow regime.