Powdery mildew (PM) is one of the most important crop diseases, causing severe economic losses to cucumber production worldwide. However, there are few reports about the proteomic response to PM infection in resistant cucumber. To understand the molecular mechanisms, the iTRAQ-based quantitative proteomics approach was employed to map the proteomes of resistant powdery mildew of the D8 (PM susceptible) and SSL508-28 (PM resistant segment substitution line) under PM inoculated (plants harvested 48 hours after inoculation) and PM non-inoculated (control) conditions.