National Interstate (NATL)

/s/  Ernst &
Young LLP

     Each of the undersigned directors of National Interstate Corporation, an Ohio corporation,
which proposes to file with the Securities and Exchange Commission an Annual Report on Form 10-K
for the fiscal year ended December 31, 2008 pursuant to the Securities Exchange Act of 1934, as
amended, and the rules and regulations promulgated thereunder, hereby constitutes and appoints
David W. Michelson, Julie A. McGraw and Arthur J. Gonzales, their true and lawful
attorneys-in-fact, as agents with full power of substitution and resubstitution for him and in his
name, place and stead, in any and all capacity, to sign in any and all capacities and file (i) such
Annual Report on Form 10-K with all exhibits thereto and other documents in connection therewith
and (ii) any and all amendments and supplements thereto, granting unto such attorneys-in-fact and
agents full power and authority to do and perform each and every act and thing requisite and
necessary to be done in and about the premises, as fully and to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all that said
attorneys-in-fact and agents, or their substitute or substitutes, may lawfully do or cause to be
done by virtue hereof.

     This Power of Attorney has been signed in the respective capacities and on the respective
dates indicated below.