Mou Zongsan's notion of "Buddhistic ontology" is interpreted here in its fundamental difference from his own previous metaphysical scheme, in the light of the Kyoto School philosophers' similar attempts to resolve the Kantian antinomy of practical reason. This is an alternative both to the analysis provided by previous interpreters of Mou's Buddhistic philosophy, such as Hans-Rudolf Kantor and N. Serina Chan, and to the comparative studies of Mou's theories with Kyoto School philosophy by Ng Yu-kwan. Previous researchers considered Mou's Buddhist philosophy in continuity with moral metaphysics. However, this idea of ontology, inspired by Tiantai perfect teaching, is essentially different from the Qixinlun-inspired scheme of "twofold ontology." The implications of this problematic idea, however, were not pursued by Mou himself, but by the next generation of philosophers, such as Wing-cheuk Chan and Ng Yu-kwan. A comparison with Kyoto School philosophy enables us to clarify how the idea of Buddhism-inspired ontology is a radical criticism against Kantian philosophy, and how it shows similarity to Nishitani's Heidegger-inspired interpretation of Buddhism, which seeks to affirm the being of all things without reserve.