Ok,tomorrow I'll try.. 
@techone: thank u for ur response..I'll use 4 optocoupler because I wanna protect both arduinos..so i use one opto for each Rx an Tx....( I don't wanna see thief who fun with overvoltage on my serial line...)
@ADI_iCoupler: oh, they sound interesting..for this projects,I'll probably use optocouplers, but in the future..