GhUGP1 (cotton uridine diphosphate glucose pyrophosphorylase) is one of the most highly expressed genes and proteins in fast elongation cotton fibres. The objective of this study was to determine whether fibre quality and reduced sugar content could be improved in fibres by over-expressing GhUGP1 in cotton plants under conditions of low autumn temperatures and large diurnal temperature differences. A plant GhUGP1 vector was constructed and introduced into the 3-6-7 cotton line using agrobacterium-mediated transformation. Following selection with kanamycin sulphate and polymerase chain reaction (PCR) and Southern blotting analyses, three independent homozygous transgenic lines were selected for molecular and chemical study. Compared with wild type, the transcriptional activity of GhUGP1 was higher and more long lasting in the transgenic lines. Fibres were longer and stronger, soluble and reduced sugar levels were significantly decreased, and cellulose levels were significantly increased. In addition, plant height also increased by 40.1-45.1%. These results demonstrate that GhUGP1 expression was considerably increased in the transgenic plants, accelerating the conversion of oligosaccharides to polysaccharides in the developing cotton fibre.