[Aim]  Planococcus vovae is an important insect pest found on cypress plants such as Juniperus chinensis and Sabina chinensis in recent years. A ladybug Nephus (Bipunctatus) koreanus is its main predator. To clarify the potential of N. koreanus as a biological control agent for P. vovae. [Methods]  We measured the predatory functional response, searching efficiency, and self-density interference response of N. koreanus 2nd-4th instar larvae and adults against different stages and ages of P. vovae under (26 ± 1) ℃, relative humidity 70% ± 5%, L∶D=14∶10. [Results]  The predation quantities on different stages and ages of P. vovae by N. koreanus 2nd-4th instar larvae and adults increased within a certain range as prey density increasing, and the predation functional responses all followed the Holling Ⅱ model. The predatory ability (a/T_h) of the N. koreanus adults against the P. vovae was greater than that of the 2nd-4th instar larvae, with 163.8, 97.7, 59.4, and 39.9 individuals respectively, and the maximum daily predation (1/T_h) was 134.9, 78.1, 48.8, and 32.0 ind./day, respectively, and followed by N. koreanus 4th instar larvae, 3rd instar larvae, and 2nd instar larvae. The searching efficiency of N. koreanus 2nd-4th instar larvae and adults on different stages and ages of P. vovae decreased with the prey density increase, and the higher the larval age, the higher the search effect was. The predatory effect of N. koreanus on P. vovae exhibits an intraspecific interference response. When the density of P. vovae remains constant at different stages and ages, the predatory rate of N. koreanus 2nd-4th instar larvae and adults on P. vovae decreases with their own density increase. This interference response conforms to the Hassell model equation. [Conclusion]  N. koreanus has strong biological control potential against P. vovae.