Thymic development of T cells is regulated by a complex network of transcription factors. Understanding these regulatory networks and the consequences they evoke is vital to determining the mechanisms underlying normal T cell maturation. One such transcription factor is Krüppel Like Factor 3 (KLF3), whose role in T cell development remains undetermined. KLF3 is a transcriptional repressor which has been shown to work in networks with other KLF family members and ETS factors. Klf3-/-mice have chronic inflammation and abnormalities in innate immune cells and splenic macrophages. Single cell RNA-seq of Klf3-/-splenocytes reveals an aberrant transcriptome in both CD4 and CD8 T cells, with upregulation of a common set of genes in both cell types. While Klf3-/-mice have normal numbers of CD4+ splenic T cells, they have significantly decreased levels of CD8+ T cells in both the spleen (Fold change = 0.57) and the thymus (Fold Change = 0.63), indicating normal CD8+ T cell development requires KLF3 expression. Mice which have mCherry tagged in-frame to Klf3 (Klf3-mCherry) displays a transient expression of KLF3 in thymocytes with expression beginning at the double negative (DN) phase, specifically DN2. Cell cycle analysis through a BrdU assay revealed Klf3-/-DN2 cells have increased proliferation compared to WT cells. This stage is normally characterised by a decrease in proliferation which allows time for TCR rearrangement to occur. We therefore hypothesise that the loss of KLF3 leads to unrestrained proliferation and aberrant TCR rearrangement at the DN2-3 stage, which causes impaired positive and negative selection, ultimately resulting in reduced numbers of peripheral CD8+ T cells.