This work reports the preparation of a novel class of lignin reverse micelles (LRM) and their application as a UV-blocking additive for thermoplastics. It is found that when 7 vol % cydohexane was added into alkali lignin (AL)/dioxane solution, LRM formed. When the cydohexane amount increased, LRM tended to aggregate and separate from the solutions. LRM films had a water contact angle higher than 80 degrees, in comparison to only 52 degrees of the AL film control sample. Due to hydrophobicity, the miscibility of LRM with high density polyethylene (HDPE) was significantly improved from that of AL with HDPE. Since LRM retained the phenolic hydroxyl structure of AL, the HDPE/LRM samples showed an excellent UV-absorbing performance. Furthermore, the added LRM had little negative influence, but significantly improved the HDPE mechanical properties. With 5 wt % LRM loading, Young's modulus increased from 1066 to 2104 MPa and the elongation at break increased from 671% to 1030%, respectively.