Antemortem serodiagnosis of aspergillosis remains challenging in Sphenisciformes. Protein electrophoresis, serology (antibody, antigen) by ELISA, and gliotoxin detection provide variable diagnostic value. In the present study, a commercially available Western blot (WB) validated for use in humans and dolphins was adapted for use with penguin samples. Using the same method and reagents, samples were analyzed from multiple institutions in the United States and one facility in France. This was inclusive of normal juvenile African penguins (Spheniscus demersus, n = 10) and various species of penguins in the United States with confirmed infection (n = 9) as well as 52 samples from Humboldt penguins (Spheniscus humboldti) in France. Cumulative WB scores (based on reactivity to different antigens) were found to be significantly higher in the group of penguins with confirmed infection (p < 0.0001). Significant differences were also observed between the clinically normal penguins in the two populations, with higher scores in the United States (median score 1.0, 95%CI [0–5], min 0, max 11) compared to France (median score 0,95%CI [0–0], min 0, max 5). The utilization of the WB as a diagnostic tool is inconclusive due to the use of samples from varying institutions, environmental background, age, and stages of infection. However, this tool may provide an overview of antigen reactivity in penguins infected with Aspergillus to help design a more robust serology assay and further understand the humoral immune response during infection.