The first to fourth generation (G1-G4) of sectorial poly(amido amine) (PAMAM) dendrimers with ethanolamine core and amino terminals are synthesized by a divergent route. Blue fluorescence emission from these dendrimers is observed. It is found that there is a remarkable difference in the fluorescence behavior for these different generations of dendrimers. The emission intensity of these dendrimers is almost linearly enhanced along with the increase of their concentrations. A significant pH-dependent profile of the fluorescence intensity is also observed. As the pH value decreases from 8 to 3, the fluorescence intensity increases almost linearly. Furthermore, the fluorescence intensity of the dendrimers shows a reversible behavior depending on pH value within the pH range from 3 to 11. This property enables the reversible manipulation of the fluorescence of these dendrimers by adjusting the pH values, which contributes to a potential application of these materials in fluorescent pH sensors.