I am using pic16f877a for relay driver interfacing program.To make the relay on,i need 5 v,what m getting from the pic is 2.25 v when i make the respective port as high .how to fix this issue
Are you using a transistor between the pics pin and the relay, I suspect not.
A relay connected directly to the pics pin will have a current need greater than the pics pin can supply so the voltage will drop when the relay tries to energise.
You can see from this link how to interface devices that need more current than a pics pin can supply.