Objective To investigate the feasibility of differentiating lymph node metastases of four types of primary tumors (lymphoma, lung adenocarcinoma, lung squamous cell carcinoma and cholangiocarcinoma) using gemstone spectral imaging (GSI) . Methods Three cases with lymphoma (28 lymph node), five cases with lung adenocarcinoma(30 lymph node), four cases with lung squamous cell carcinoma(24 lymph node) and two cases with cholangiocarcinoma( 10 lymph node) were evaluated by germstona spectra imaging CT scans. Imaging protocol included unenhanced conventional CT scan (120 kVp) ,enhanced GSI (80/140 kVp) on arterial phase and conventional CT scan (120 kVp) on portal phase. CT attenuation values of lymph nodes in the monochromatic images at 11 sets of keV levels (40-140 keV, 10 keV step) and the iodine and water contents of these lymph nodes were measured. All results were analyzed with ANOVA and t test. Results The optimal monochromatic level was 70 keV for the optimal contrast-noise ratio (CNR) of metastatic lymphadenopathy. The CT attenuation values of metastatic lymphadenopathy were (81.36 ±9. 81 ), (58.33 ± 21.55 ), (56. 47 ± 10.62) and (73. 57 ±4. 43 ) HU,respectively, at 70 keV( F = 17.29, P ＜0. 01 ). There were significant differences in CT attenuation values between lymphoma and lung adenocarcinoma, between lymphoma and lung squamous cell carcinoma and between lung squamous cell carcinoma and cholangiocarcinoma (P ＜ 0. 05 ). The differences in CT attenuation values were significant between cholangiocarcinoma and lung squamous cell carcinoma, between cholangiocarcinoma and lymphoma ( P ＜ 0. 05 ). There was no difference in CT attenuation values at all 11 sets of keV levels between lung squamous cell carcinoma and lung adenocarcinoma ( P ＞ 0. 05 ). The iodine contents of lymphoma, lung adenocarcinoma, lung squamous cell carcinoma and cholangiocarcinoma were ( 1. 93 ± 0. 04 ), ( 1.16 ± 0. 15 ), ( 1.25 ± 0. 21 ) and ( 1.44 ± 0. 04 ) g/L, respectively. The water contents of lymphoma, lung adenocarcinoma, lung squamous cell carcinoma and cholangiocarcinoma were (1029.40 ± 20. 85), (1024.98 ± 11.19), (1022.12 ± 12. 94) and (1030.87 ± 10.10) g/L,respectively. Except between lung squamous cell carcinoma and lung adenocarcinoma, the differences in the iodine contents of metastatic lymphadenopathy were significant among tumors ( P ＜ 0. 05 ). There was no difference in the water contents of metastatic lymphadenopathy among tumors ( P ＞ 0. 05 ). Conclusions Although CT spectral imaging fails to differentiate metastatic lymphadenopathy of lung adenocarcinoma and lung squamous cell carcinoma, it is also a promising method of distinguishing metastatic lymphadenopathy of malignant tumors by CT attenuation values in monochromatic images and iodine contents in material density images. The optimal monochromatic level was determined to be at 70 keV for providing the optimal CNR of metastatic lymphadenopathy.