The mafic dyke swarms in Mugua-Chun’an area, Zhejiang Province mainly consist of diabase and diabase porphyrite with NW-SE trend. The rocks are mainly tholeiitic according to geochemical analyses. The REE distribution patterns show strong LREE-enrichment, with (La/Yb)N ratios of 5.1~7.6 (mean=6.36), indicating a strong fractionation between LREE and HREE and possible residual garnet in the source region. The La/Sm vs. La diagram shows that the mafic dyke swarms in this region are mainly the production of equilibrium partial melting. The Eu anomaly is not obvious (δEu=0.95~1.03, with an average value of 0.99), reflecting that there was no prior plagioclase separation from the source region. Furthermore, the mafic dyke swarms are enriched in LILE (K, Rb, Cs, Ba, Sr) and HFSE (Nb, Ta, Zr, Hf, Ti) compared to mid-ocean ridge basalt.