Background The Theory of Planned Behavior (TPB) has been extensively used to examine donation intentions in the general community. This research seeks to examine whether TPB applies to one culturally and linguistically diverse (CALD) community in Australia and also incorporates blood donation knowledge as an antecedent in the model, given that the TPB assumes people make informed decisions regarding blood donation. Study design and methods A cross-section of 425 members of African CALD communities was surveyed face to face using bilingual workers, ensuring inclusion across literacy levels within the CALD community. Constructs used within the survey were drawn from the TPB blood donation literature (i.e., attitudes, social norms, and self-efficacy). A new measure of blood donation knowledge was included. Results Structural equation modeling found that the Basic TPB model did not hold for African CALD communities in Australia. The Basic TPB model was modified and within this Adapted TPB model attitudes were found not to impact intentions directly, but had a mediating effect through self-efficacy. An Extended TPB model including overall knowledge was then tested and improved the model fit statistics, explaining 59.8 variation in intentions. Overall knowledge was found to indirectly impact intentions, through self-efficacy, social norms, and attitudes. Conclusion The TPB applies differently when examining African CALD communities blood donation intentions in Australia. Knowledge is an important mediating component of the Extended TPB model rather than directly affecting intentions. Addressing CALD communities psychographic characteristics may assist blood services in developing targeted strategies to increase donations within these communities.