  We show that, without any extra physical degree introduced, the Standard
Model can be readily reformulated as a Double Field Theory. Consequently, the
Standard Model can couple to an arbitrary stringy gravitational background in
an $\mathbf{O}(4,4)$ T-duality covariant manner and manifest two independent
local Lorentz symmetries, $\mathbf{Spin}(1,3)\times\mathbf{Spin}(3,1)$. While
the diagonal gauge fixing of the twofold spin groups leads to the conventional
formulation on the flat Minkowskian background, the enhanced symmetry makes the
Standard Model more rigid, and also stringy, than it appeared. The CP violating
$\theta$-term may no longer be allowed by the symmetry, and hence the strong CP
problem is solved. There are now stronger constraints imposed on the possible
higher order corrections. We speculate that the quarks and the leptons may
possibly belong to the two different spin classes.
