Hi nurulrusli,
nurulrusli WROTE:hello..may i know what is suitable rfid to be used with existing card such as student card. mifare or RFID Reader RS232. tq

You need to know what type of existing card you want to use. I think it is not easy to use your student card as part of your project since there have an important data used by your University/College. Unless you do a collaboration with them.
Mifare Reader/Writer CR038: able to read and write Mifare card.
RFID Reader RS232 (New): only read 125kHz RFID card.