Abstract: Abstract: 【Objective】The study aimed to elucidate the fiber morphological characteristics, as well as the underlying mechanisms, in Pseudosasa japonica var. tsutsumiana, a stable dwarf variant of P. japonica. 【Method】 Microscope observation and paraffin sections were used to compare cell morphology. Relative transcript abundance was measured by quantitative reverse transcription polymerase chain reaction(qRT-PCR), and ultra performance liquid chromatography/gas chromatography-mass spectrometry(UPLC/GC-MS)was used to investigate gibberellin(GA)abundance. 【Result】 Values for fiber length, the ratio of length to width, and the runkel ratio were significantly smaller in P. japonica var. tsutsumiana culm than in P. japonica. However, the width and lumen diameter values of the variant fiber were larger than that in the wild type. Although the fiber cell wall thickness in different culm parts of P. japonica var. tsutsumiana was smaller than those in P. japonica, the difference was statistically insignificant. In addition, the fiber length, length to width ratio, cell wall thickness, and runkel ratio in P. japonica var. tsutsumiana rhizomes were also significantly smaller than those in P. japonica. Similar to the culm, the values for width and lumen diameter in the rhizome fibers of the variant were larger than those of the wild type. Anatomical analysis revealed that irregular phenotypes of fiber cells in P. japonica var. tsutsumiana clearly emerged at the initiation stage of internode elongation. Relative gene expression level measurements of the GA, cell wall growth and cytoskeleton-related genes on the internodes at different elongation stages showed that the GA pathway in P. japonica var. tsutsumiana was inhibited at the early stage of internode growth, and that genes relating to cell wall and cytoskeleton organization were significantly downregulated on the internode during the active growth stage of the variant. Compared with the wild type, the GA content was indeed lower at the internode in the early elongation stage of P. japonica var. tsutsumiana, as was further demonstrated by the qRT-PCR results. 【Conclusion】The inhibition of the GA signal pathway, which results in the downregulation of its downstream genes, such as those related to cell wall growth and cytoskeleton organization, is one of the factors that causes abnormal growth of fiber cells in P. japonica var. tsutsumiana.