Abstract: Objective To explore the relationship between expression of human platelet factor 4（hPF4）mRNA, concentration of Plasma PF4 and cervical lymph node metastasis in papillary thyroid carcinoma(PTC). Methods RT-PCR technique was utilized to detect the expression of hPF4 mRNA in 40 cases of PTC and 10 cases of normal tissue surrounding carcinoma. Meanwhile enzyme-linked immunosorbant assay(ELISA) technique was used to measure the concentration of PF4 in plasma of all 40 patients with PTC and 20 healthy persons as control. Results (1)The positive expression rate of hPF4 mRNA of PTC and normal tissues was 47.5% and 80%，respectively. The positive expression rate of hPF4 mRNA of PTC tissue was significantly lower than that of normal tissues(P<0.01). Furthermore the metastatic rate of cervical lymph node of PTC with hPF4 mRNA positive expression was significantly lower than that of PTC with hPF4 mRNA negative expression (36.84% vs. 90.48%)(P<0.01). (2) The concentration of PF4 in plasma of normal healthy person, PTC with cervical lymph node metastasis and PTC without cervical lymph node metastasis was in linear progressive decreasing tendency. The plasma concentration of PF4 in PTC without cervical lymph node metastasis［(2.96±0.21)ng/ml］ was higher than that in PTC with cervical lymph node metastasis［(0.98±0.17)ng/ml］(P<0.05). (3) The plasma concentration of PF4 in PTC with hPF4 mRNA positive expression was higher than that in PTC with hPF4 mRNA negative expression［(2.49±0.83）ng/ml vs. (0.94±0.13)ng/ml］(P<0.01). Conclusion The decline of the level of plasma PF4 and local lesion of PTC may be one of the reasons which can cause or promote cervical lymph node metastasis of PTC.