The wide applications of titanium dioxide nanoparticles (TiO2 NPs) increase the possibility of their exposure to ecosystems， and therefore an improved understanding of their effects to organisms is required. However， their potential toxicity on eukaryotes， especially fungi， needs further detailed investigation. Here， we investigated the effects of anatase TiO2 NPs on the reactive oxygen species (ROS)-scavenging system in the model fungal organism， Pichia pastoris. Results showed that the NPs entered cells and had toxicity to this fungus， and their toxicity was attributed to cell wall damage， cell membrane damage， and ROS accumulation， but not apoptosis or autophagy. Interestingly， the synthesized TiO2 NPs impaired but not activated the ROS-scavenging system， which contributes to the cytotoxicity. Moreover， this impairment was associated with down-regulation of antioxidant-related genes， especially those genes involved in GSH regulation. Hence， GSH may play a key role in the interaction between TiO2 NPs and yeast cells.