Penicillium expansum, the causal agent of blue mould of pome fruits, is a major postharvest pathogen in all producing countries. To develop a better understanding of disease resistance mechanisms in apples, a comprehensive transcriptional analysis of apple gene expression in response to a compatible (P. expansum) and non-host (Penicillium digitatum) pathogen was conducted using an apple microarray of approximately 40,000 probes. The resulting data provide further evidence that apples inoculated with P. expansum exhibit significant upregulation of defense-related genes and genes involved in detoxification of reactive oxygen species. In contrast, apples inoculated with P. digitatum, a non-host pathogen, exhibited upregulation of genes involved in phenylpropanoid metabolism. To confirm the accuracy of the expression profiles obtained with the microarray, reverse transcriptase-quantitative polymerase chain reaction was conducted for four genes specifically in the phenylpropanoid pathway. Expression data was obtained for different time points and fruit maturity stages. The highest expression level of the phenylpropanoid genes was detected 48 h after inoculation with P. expansum in both immature and mature apples. These results support the hypothesis that apples respond in a complex and diverse manner to the compatible compared to the non-host pathogen. To the best of our knowledge, this is the first study in apple fruit that has conducted an analysis of global changes in gene expression in response to a compatible (P. expansum) and non-host (P. digitatum) pathogen.