Microchannel (MC) emulsification is a novel technique for producing monodispersed emulsions. In this study, we investigated the effect of interfacial tension and viscosities of the dispersed and continuous phases on the droplet formation behavior with various surfactant concentrations and various dispersed and continuous phases. Experimental results showed that interfacial tension did not greatly affect the resultant droplet diameter, while the viscosities of both phases had significant effects. Droplet diameter increased with increasing viscosity ratio between the dispersed and continuous phases but did not change in the case of constant viscosity ratio. These results indicated that the droplet diameter is controlled by the viscosity ratio when the MC structure is identical. On the other hand, detachment times increased with increasing viscosities of dispersed and continuous phases. This indicated that the emulsion productivity would decrease with increasing viscosities of the two phases.