Can I write blog on Facebook?

No you can't but you can update your status.

2007-07-27 06:04:42 補充：
Sorry I am wrong, just need to correct my answer. You can indeed to write blog on facebook. You need to add the 'blog' application and you can set up you own blog. If you already have a blog on another site, you can add 'blog link' application to set up a link from the facebook.

yes you can but not on in the name of blog

you can write NOTES!! same thing!! your friends will still be notified!!