MiRNA are non-coding RNAs with 19～25 nucleotides in length, which play an important role in regulation of gene transcription and translation and greatly contribute to the development of tumor and cardiocerebral vascular diseases. Recently studies show that miRNAs stably exist in the peripheral blood. Changes of miRNA levels in the circulation are closely related to the occurrence, development and prognosis of multiple diseases. Therefore miRNAs may be a novel class of biomarkers for diseases. Plant-derived miRNAs can also stably exist in the blood and participate in the regulation of many target proteins of animals. It is of great significance to assess the efficacy of traditional Chinese medicine and to clarify the underlying mechanisms through examining the changes of plant-derived miRNA levels in the blood.