We report on new stable polymerized fullerites consisting of large fullerenes. Using the empirical many-body model potential for C atoms, we find that C-74 and C-78(C-2 nu') fullerenes possess stable infinite covalent networks in which C-74 and C-78 fullerenes form two-dimensional hexagonal lattice and one-dimensional chain, respectively. These phases are lower in energy than C-60 polymers known to date. Moreover, in each case, the energy gain upon the interfullerene-bond formation is larger than that of the C-60 polymer. Also their dimers, (C-74)(2) and (C-78)(2), are found to be highly stable. Based on the tight-binding study, they are both found to be semiconducting.