In this study, the effect of a tackifier on the viscoelastic and adhesion properties of acrylic pressure-sensitive adhesives (PSAs) was investigated. The intermediate products in the process of PSA synthesis, including an acrylate-based copolymer solution, a cross-linked copolymer, and the final product with a tackifier, were prepared and characterized using dynamic mechanical analysis (DMA). A significant increase in storage and loss moduli at high angular velocities was observed for the final product with the tackifier. The adhesion forces of the copolymer solution and the cross-linked copolymer measured by atomic force microscopy (AFM) were found to be almost independent of the release velocity, whereas that of the final product with the tackifier significantly increased at higher release velocities because of viscoelastic effects. Their fibrillations during the release process were also visualized using a charge-coupled device (CCD) camera installed on the cantilever holder. Although the contact area of the copolymer solution and the cross-linked copolymer with the probe surface decreased until detachment, the final product with the tackifier remained constant, with necking just below the probe surface. The increased storage and loss moduli were considered to resist the shrinkage of the contact area because the contact outline was subject to high shearing deformation, which led to localized high strain rates. Overall, the crucial role of the tackifier in maintaining the contact area for sufficient elongation during fibrillation was established.