I had read a post in this forum somewhere about FTP log
file, but I can find that post now.
I want to know is from which log file I can find who and
when he/she uploaded files from IP xx.xx.xx.xx.
Anybody know that log file?

Thanks in advance.

Without looking at it, and from memory, I think it is at:

/var/log/xferlog

-if that isn't correct, I wouldn't be surprised, but try that. I'll check into it later and edit this once I find out for sure.