> Whenever the 5V output from PIC is applied to relay, the microprocessor
>will run unexpectedly. If I put relay in a separated board, it's OK. I think
>the problem is the noise from the inductance of relay. Can anyone tell me
>how to eliminate this problem? Thank you.

  Hi Peter. I'll try not to avoid the dyslexia that plagued me
  Sunday when I tried to help someone else with a similar problem.
  :-(

  If you could find a relay that would operate on 20mA of current,
  you could theoretically drive it direct from the PIC, but it
  would still be a bad idea.

  Don't drive the relay directly. Drive the base of a switching
  transistor thru a series resistor. For a typical low voltage
  relay, use a 2N2222 and put the relay in the collector circuit.
  Use a 470 ohm resistor to drive the base. In parallel with
  the relay coil, place a general-purpose diode with the CATHODE
  toward the (+) supply voltage.

  It's a good idea to return the (-) side of the relay supply
  directly to the transistor emitter, which should also be
  logic ground.

  Make sure that MCLR is asserted high and that your supply will
  deliver the current your circuit is demanding from it.

  If that doesn't stop the resets, email me directly and I'll
  try to help you further.

  Reg Neale