miRNAs (microRNAs) are a type of conserved,endogenous and non-coding small RNAs in plants,and regulate their target genes at post-transcriptional level,which plays important roles in plant.Poncirus trifoliata is a cold-tolerant citrus relative and is often used as rootstock in citrus industry.The mature sequence and precursor sequence were identified in this study.The results showed that ptf-miR168a sequence was highly conserved in plants.The target genes of ptf-miR168a were analyzed and predicted to be NAC transcription factors and zinc finger genes.The over-expression vector was constructed and transformed to tobacco.A total of 18 transgenic lines were obtained.It will provide valuable materials for further studying the regulatory role of ptf-miR168a in response to cold stress.