With-No-Lysine kinases (WNK) have been reported to be associated with plant growth regulation in Arabidopsis, soybean, and rice, but little is known of their roles in fruits.In this study, a total of 114 WNK genes were identified from 8 fruit trees species, and these WNK genes be-longed to 2 classes (I and II) that respectively contain 4 (A, B, C, D) and 2 groups (E, F).The WNK genes had variable exon-intron structures and were randomly distributed among most chromosomes of each genus.The expression levels of six of the 18 WNK genes in peach were almost undetectable in fruits, suggesting that they may not be associated with fruit development and ripening.Of the other 12 WNK genes, PpWNK.B1 exhibited stronger stability of expression levels than the best reference genes reported previously in fruits from two peach cultivars.These results suggested that PpWNK.B1 could be a reliable reference gene for gene expression studies of peach fruit.Moreover, qRT-PCR assays yielded evidence that when using single reference gene as internal control, mistakes were more possible, indicating that the use of three reference genes is necessary for gene expression studies.Based on the gene expression profiles validated by qRT-PCR, PpWNK.A1 is predicted to likely be involved in fruit ripening, while PpWNK.A2 and PpWNK.E3.1 are likely associated with early fruit development.The present study represented the WNK genes in fruits, and it will be a valuable resource in continuing investigation of gene regulation network during fruit development and ripening.