The microwave excited emission spectrum of gaseous ZrO has been recorded with a Fourier transform spectrophotometer in the region 8500 to 12 000 cm −1. The b′ 3II- a 3Δ system, which consists of a single (0, 0) sequence located around 10 700 cm −1, been reinvestigated. As distinguished from an earlier analysis of this system, the present rotational analysis ascribes every spectral feature around 10 700 cm −1 to the b′ 3II- a 3Δ system. The analysis includes branches from the (0, 0), (1, 1), and (2, 2) bands. No satellite transitions were observed. Molecular constants have been determined for the two states. The fit to the bottom state also includes branches of the c 3II- a 3Δ system of ZrO. Only the most abundant isotopomer 90ZrO is treated. The origin of the rather large A-type doubling of the b′ 3II state is discussed in terms of the nearby theoretically predicted but experimentally unobserved 3Σ − state. The triplet splitting parameters of the upper state are compared to semiempirical estimates.