For completely contractive Banach algebras A and B (respectively operator algebras A and B), the necessary and sufficient conditions for the operator space projective tensor product A ⊗B (respectively the Haagerup tensor product A ⊗ h B) to be Arens regular are obtained. Using the non-commutative Grothendieck's inequality, we show that, for C * -algebras A and B, the Arens regularity of Banach algebras A ⊗ h B, A ⊗ γ B, A ⊗ s B and A ⊗B are equivalent, where ⊗ h , ⊗ γ , ⊗ s and ⊗ are the Haagerup, the Banach space projective tensor norm, the Schur tensor norm and the operator space projective tensor norm, respectively.