flash drive query

i think no

No. Rather it makes the drive useless!

Which is the default file system of the Flash/Pen drives?

Most of flash drives use FAT format.
Formatting FAT to NTFS is recommended and can be done without problems.

No Dont Change It To Fat32

okie thnx
ill keep it at fat
and my usb cant be formatted to ntfs

I am having Kingston Datatraveler. Will it do any good formatting it to NTFS?

There are some things which you need to be aware of before changing the format to NTFS. All memory stick devices are formatted to either FAT or FAT16 or FAT32. The advantage of FAT16 or FAT32 format lies w.r.t Windows. Windows disables "write caching" on flash devices. With FAT format you can remove the flash drive as soon as read/write is done. You need not worry much about the Windows safe removal process. Many a times we neglect the safe removal process and just unplug the device. In such scenario's stick to FAT format.

Once formatted to NTFS, You need to carry on the Windows safe removal process perfectly. Else the device may easily get damaged.
The advantage in NTFS system is that you get a huge performance boost while dealing with small size files. For larger file sizes, it is not recommended becoz NTFS uses many read/write cycles.

Summarizing above..
Small file sizes transfer: Use NFTS format
More Data reliability: Use NFTS format

If above is your scenario, proceed to NTFS format. Else stick to FAT.

Thank you Kiran but always I use the safely remove method.

My pleasure!
Its always good to follow the safe removal process. But what about file size in the device? If it is big transfers, stick to FAT.