We show that the star formation activity of spiral galaxies has a great variety. The star formation variation in a time scale of 10 8 yr and the mechanism responsible for the variation are discussed.

We construct a simple photometric evolution model of galaxies based on the evolutionary population synthesis. In our models an exponentially decreasing SFR with a power law IMF is used to compute the UBV colors of galaxies from ellipticals to late type spirals. It is shown that the integrated colors of galaxies with different Hubble type can be explained by one parameter, SFR.