A simplified method was proposed for separately evaluating a fouling mechanism and a fouling degree in constant pressure dead-end microfiltration from limited flux decline data in reference to the conventional indices such as the silt density index (SDI) and the modified fouling index (MFI). Two indices were proposed: one is the fouling mechanism index (FMI) estimating the fouling mechanism; the other is the fouling degree index (FDI) evaluating the fouling degree. Both indices were calculated from the measurements of filtrate volumes collected during a given time interval at two different filtration times and analyzed based on the blocking filtration law involving the cake filtration mechanism. Moreover, these indices well evaluated the variation over time of the flux decline throughout the course of filtration in dead-end microfiltration. The usefulness and validity of the indices were verified from microfiltration experiments of a variety of colloids ranging from nanometer- to micrometer-size.