Partial wave resonances, quasi-bound resonance states with well-defined rotation in the transition state region of a chemical reaction, play a governing role in reaction dynamics but have eluded direct experimental characterization. Here, we report the observation of individual partial wave resolved resonances in the F + HD -> HF + D reaction by measuring the collision energy-dependent, angle-and state-resolved differential cross section with extremely high resolution, providing a spectroscopic probe to the transition state of F + HD -> HF + D. The agreement of the data with the high-level theoretical calculations confirms the sensitivity of this probe to the subtle quantum mechanical factors guiding this benchmark reaction.