  This paper is devoted to deriving the Onsager-Machlup action functional for
Mckean-Vlasov stochastic differential equations in a class of norms that
dominate $L^2([0,1], \mathbb{R}^d)$, such as supremum norm
$\|\cdot\|_{\infty}$, H$\mathrm{\ddot{o}}$lder norms $\|\cdot\|_{\alpha}$ with
$\alpha<\frac{1}{4}$ and $L^p$-norms with $p>4$ are included. Moreover, the
corresponding Euler-Lagrange equation for Onsager-Machlup action functional is
derived and a example is given.
