I have to travel from Tokyo to Sapporo using the JR Pass on the night of 27 July 2013. May I know whether it will be
possible and convenient or not. Is there any night train which I can choose for my this travel?
Tokyo to Sapporo night travel

Hi there,
There's a couple of options available for you here:
One, is to take the Cassiopeia/Hokutosei train from Tokyo directly to Sapporo. This service is however does require a substantial charge, as the JR Pass is not valid for sleep compartments on this train and part of the journey is traveled on private railway. You can find more information about fares here.
The 2nd option is to take the Akebono train from Tokyo (Ueno station) which arrives the following morning in Aomori. From here you can take a day service to Sapporo. The nice part about this route is that it is free with the JR Pass.
A 3rd option is to take the Shinkansen (Bullet Rail) to Aomori and take the Hamanasu night train from there, which arrives in Sapporo the following morning. A basic seat in this train is covered by the JR Pass.
Do note that night trains are rather popular and can sell out quickly. So be sure to book in advance if you can.
I hope this helps,