Abstract Mingliutianju (Citrus reticuiata Blanco cv.Mingliutianju, MP) is a novel late ripening cultivar selected from Chuntianju (Citrus reticuiata Blanco cv.Chuntianju, CP) through spontaneous bud mutation. Large-scale analysis of gene expression differences between of peels of MP and CP is studied during the course of 12 weeks and 23 weeks after flowering (WAF) using Affymetrix GeneChip® citrus genome array to provide new insights into the mechanisms behind this bud mutation. Altogether, 395 differentially expressed genes are identified including 132 up-regulated and 263 down-regulated genes. Singular enrichment analysis (SEA) and parametric analysis of gene set enrichment (PAGE) are performed and 7 statistically significant differentially expressed genes are selected finally for further study. Results from semiquantitative RT-PCR performed on these 7 genes show that one gene's expression situation is totally correlated with that observed with the microarray. These seven genes include three UDP-glucosyltransferase genes, two disease resistance-responsive protein-related genes, one chitinase gene and one protein kinase family protein gene, all of which are involved in 18 different biological processes according to the hierarchical tree of annotated gene ontology (GO) terms. The candidate biological process and its relation to bud mutation are discussed.