can we use a pic16f project board to pic18f,both are 40pin dip package..?are should i build a new one.

thanks in advance.

 

Only if the pins have the same labels and functions. Chances are vanishingly small.

 

Have you consulted each Pic manual?
There are 18F versions where the pins are multiplexed (re-assignment possible) if necessary.
Max.

 

Microchip loves to keep the same pinout between devices, so it is extremely possible you can do this.

Of course, you need to check each and every pin to insure they are compatible.