How to transmit pure binary by UART?

Hi, I want to transmit hex 'FF'(11111111) from one arduino to another arduino by xbee.
But the UART always transmit ascii code , there is not any ascii code of FF, is there any solution?
Can I transmit any binary without transforming to ascii code by UART?

Serial.write(0xff);

can I trans it by serial monitor?

I don't understand the question.

The UART sends any byte that you tell it to send, binary or ASCII. So do any of the several variations of software serial.

yangkai:
can I trans it by serial monitor?

Assuming that means can you transmitt 0xff from the serial monitor then the answer is no. The serial monitor is a keyboard ASCII based application. Other terminal emulators allow you to send files, so use one of those and send a file with just one byte in it.

You can always send the text FF or 0xFF from the serial monitor, use the Arduino to convert it to a number (255, 0xFF) and send that to the XBee. Have a look at e.g. the atoi() function.

And just in case, read Serial Input Basics - updated.

// Edit
maybe the strtol() is better suited; not tested so OP needs to try.