May or may not be accurate, but according to this site: http://www.htmlite.com/mysql003.php.
BLOB A string with a maximum length of 65535 characters.
The MySQL manual says:
The maximum size of a BLOB or TEXT object is determined by its type, but the largest value you actually can transmit between the client and server is determined by the amount of available memory and the size of the communications buffers
I think the first site gets their answers from interpreting the MySQL manual, per http://dev.mysql.com/doc/refman/5.0/en/storage-requirements.html
A BLOB can be 65535 bytes maximum. If you need more consider using a MEDIUMBLOB for 16777215 bytes or a LONGBLOB for 4294967295 bytes.
Hope, it will help you.
A BLOB can be 65535 bytes (64 KB) maximum.
If you need more consider using:
a MEDIUMBLOB for 16777215 bytes (16 MB)
a LONGBLOB for 4294967295 bytes (4 GB).
See Storage Requirements for String Types for more info.
Source: Stackoverflow.com