Brown dog tick (Rhipicephalus sanguineus) infestations have long been a problem in the Philippines due to the warm surroundings and high population of dogs (Dantes-Torres, 2010; Nag, 2017). To address the natural and aggravating situation, scientists have started formulating acaricides; however, there were always environmental, economical, or clinical downsides. With this, the researchers aimed to create an acaricide using the growing concept of green nanotechnology. Hence, the researchers biosynthesized guyabano-mediated Copper nanoparticles (CuNPs) and determined its acaricidal potential. Specifically, it sought to find the answer to the questions: (1) What are the bioactive compounds present in the guyabano leaf ethanolic extract?; and (2) Is there a significant difference in the mortality rate of Rhipicephalus sanguineus within the experimental group and between the experimental and control groups. The researchers utilized a Completely Randomized Design and used One-Way ANOVA for data analysis. Guyabano leaves were extracted using ethanol and the maceration method. The researchers then conducted a qualitative phytochemical analysis wherein they found out that alkaloids, terpenoids, proteins, and tannins are present in the guyabano leaf ethanolic extract. Moreover, the researchers utilized an in vitro bioassay to determine the mortality rates of brown dog ticks and discovered that different concentrations of guyabano-mediated CuNPs (5%, 10%, 20%, 30%, 40%) can successfully exterminate brown dog ticks in a span of four hours, with 30% as the fastest under 100 minutes. Although, they are still significantly slower than established commercial acaricides (Amitraz) and showed no significant difference between the varying concentrations of CuNPs.