A controlled polymerization strategy is developed by confining the step-growth polycondensation to take place exclusively in the nanochannels of dendritic mesoporous silica nanoparticles. A variety of conjugated polymers with rich structural patterns were obtained in high yields. The molecular weights were precisely controlled with narrow molecular weight distributions. The obtained conjugated polymers were freely processed in solution and casted in film, showing bright fluorescence emission. All the features of this controlled polymerization method endow the conjugated polymers great potential for future applications.