A new system belonging to the emission spectrum of PtO has been found in the region of 3800–4500 Å. This system has the earlier known X1Σ ground state as the lower state and a hitherto unknown 1Σ state, here designated the D1Σ state, as the upper state. The four lowest vibrational levels of the D1Σ state were rotationally analyzed. Of these levels, the [Formula: see text] level seems to be unperturbed although the v′ = 1, 2, and 3 levels are strongly perturbed.