Thanku, balupton.
Well. I am using Vietnamese UTF-8, and I lost such a day to discover why I couldn't wirte post with my own language. And, the answer is, I have to set b2evolution\blogs\conf\_advanced.php

$db_config['table_options']

into

$db_config['table_options'] = ' ENGINE=InnoDB DEFAULT CHARSET=utf8';

With amature, they will lost far more than a day!
So why don't we recognize whenever the table should have specify charset?
It's really easy, just 10' editing some codes...