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The KNOX transcription factor plays crucial roles in regulating fiber growth in plants. Although the genome of ramie, an important fiber crop in China, is available, knotted related homeobox <i>(KNOX</i>) genes have not been systematically explored in this crop. In this study, seven members of the <i>KNOX</i> gene from the ramie genome were identified and assigned to two groups, Class I and II. The intron–exon structure, conserved domain architecture, cis-regulating elements, and expression pattern showed distinct differences among the seven KNOX regulators. One of the genes, <i>Bnt07G011994</i>, encodes an ortholog of <i>Arabidopsis</i> fiber-growth-related KNAT7, and is differentially expressed among barks undergoing different stages of fiber growth. The overexpression of <i>Bnt07G011994</i> dramatically decreases the fiber number in transgenic <i>Arabidopsis</i>, indicating a negative role played by this gene in modulating fiber growth. Further transcriptome analysis of transgenic <i>Arabidopsis</i> revealed that the overexpression of <i>Bnt07G011994</i> resulted in an expression change in 14 pectin biosynthesis-/metabolism-related genes. These findings provide a useful foundation for further investigating the function of <i>KNOX</i> genes in ramie, and provide an important insight into the involvement of the ramie <i>KNOX</i> gene in fiber growth.