  We provide arguments for the property of the degree-degree correlations of
giant components formed by the percolation process on uncorrelated random
networks. Using the generating functions, we derive a general expression for
the assortativity of a giant component, $r$, which is defined as Pearson's
correlation coefficient for degrees of directly connected nodes. For
uncorrelated random networks in which the third moment for the degree
distribution is finite, we prove the following two points. (1) Assortativity
$r$ satisfies the relation $r\le 0$ for $p\ge p_{\rm c}$. (2) The average
degree of nodes adjacent to degree-$k$ nodes at the percolation threshold is
proportional to $k^{-1}$ independently of the degree distribution function.
These results claim that disassortativity emerges in giant components near the
percolation threshold. The accuracy of the analytical treatment is confirmed by
extensive Monte Carlo simulations.
