  We investigate a regularity for weak solutions of the following generalized
Leray equations \begin{equation*} (-\Delta)^{\alpha}V-
\frac{2\alpha-1}{2\alpha}V+V\cdot\nabla V-\frac{1}{2\alpha}x\cdot \nabla
V+\nabla P=0, \end{equation*} which arises from the study of self-similar
solutions to the generalized Naiver-Stokes equations in $\mathbb R^3$. Firstly,
by making use of the vanishing viscosity and developing non-local effects of
the fractional diffusion operator, we prove uniform estimates for weak
solutions $V$ in the weighted Hilbert space $H^\alpha_{\omega}(\mathbb R^3)$.
Via the differences characterization of Besov spaces and the bootstrap
argument, we improve the regularity for weak solution from
$H^\alpha_{\omega}(\mathbb R^3)$ to $H_{\omega}^{1+\alpha}(\mathbb R^3)$. This
regularity result, together linear theory for the non-local Stokes system, lead
to pointwise estimates of $V$ which allow us to obtain a natural pointwise
property of the self-similar solution constructed in \cite{LXZ}. In particular,
we obtain an optimal decay estimate of the self-similar solution to the
classical Naiver-Stokes equations by means of the special structure of Oseen
tensor. This answers the question proposed by Tsai \cite[Comm. Math. Phys., 328
(2014), 29-44]{T}.
