Hi Electronics_Kumar,
I don't really get what you want, but I thikn this'll make it more clear for you.
In some applications, we prefer blocking the DC and amplify only the small signal AC signal. This is also used in multistage cascaded amplifiers, where we don't want the DC level of one of the stages to alter or affect the biasing of the following stages, i.e. isolate them and in the same time pass the AC signal without the use of a bulky transformer.
Sometimes, we even want to pass the DC and block the AC, for example, in VCO's making use of Varactors so we use a coil with high inductance or whats commonly known as a RF Choke coil.