A detailed study of the Ofpe/WN9 candidate MCA1b in M33 (Willis et al. 1992) is presented, based on new high-resolution observations. We re-classify MCA1b as WN9-10 and determine its physical parameters (T * = 29 kK, logL/L⊙ = 5.9, log· = −4.0, v ∞ = 420 km s−1) and composition (H/He = 2.6, N/He = 0.003, C/N = 0.2) using the Wolf-Rayet standard model. Overall, MCA1b is very similar to the LMC stars R84 (WN9, Crowther et al. 1994) and R71 (LBV, Lennon et al. 1994) indicating a similar evolutionary status and metallicity.