Dear Mahesh,
The characteristic for the RFID card reader that i'm using is 2400 bauds/sec ,8 bits,no parity,1 stop bit.Each tag has a unique ID of 12 bytes,the first 0A and the last 0D.
I've checked how the reader is transmitting by connecting it to the PC via a MAX232 interface and the results are shown in picture below.

http://rapidshare.com/files/237356283/3.jpg.html

After that i've connected the rfid to the 89s52: the SOUT pin to RxD pin of 89s,the GND&/ENABLE pins to gnd and the VCC pin to +5v.The reader is powered-up and transmitting becuse the on-board led is RED(as stated in datasheet)

What my code is trying to do is make the 89s get a tag ID from the reader,to see if it starts with 0A and ends with 0D and if so to make a LED glow.

I think the problem is here

START_RX:
               JNB 00h, WAIT_RX
               MOV @R0,A
               CJNE R0,#4Ah,INC
 

i don't know were to go if i already received 10 bytes

I've also tried the code u provided and i get an error when making the hex file

CMP_NXT:
               MOV A,R2
               MOVC A,@A+DPTR
               CJNE A,@R0,NO_MATCH  ;the error is at this line "Undefined symbol/label"