We found that the dynamic mechanical spectra of linear high-density polyethylene (HDPE) can be controlled by swelling using liquid paraffin (LP) at 100 and 110 degrees C. The relaxation strength of alpha relaxation observed above 50 degrees C decreased with an increase in swelling time. Two novel peaks appeared between gamma and alpha relaxations, denoted as beta(1) and beta(2) on the lower temperature side, respectively. These peaks are absent in pristine HDPE and are associated with the immersion of LP molecules in the amorphous phase. beta(1) appeared at approximately -50 degrees C and was almost independent of frequency; it is believed to be responsible for the glass transition of LP domains. Meanwhile, beta(2) appeared at approximately -20 degrees C, similar to the beta-relaxation temperature observed in linear low-density polyethylene (PE) and ultrahigh molecular weight PE. beta(2) was responsible for the activation of molecular motion in the rigid amorphous chains, such as taut tie-chains in the interlamellar regions, in which the addition of LP expanded the amorphous layers and caused surface melting of the crystalline lamellae.