To investigate the effect of dimethoxymethylsilyl-terminated polypropylene oxide (DMSi-PPO) elastomer particles on the toughening of epoxy resin, the particles were prepared in liquid bisphenol A-type epoxy resin by means of the dynamic vulcanization method. With the addition of aminosilane (AMS), the fracture energy G(1c) values of adhesive joints and the T-peel bond strength were more than three times those of the unmodified system without a decrease in T-g. Observations of the modified epoxy resin before curing using a video microscope revealed that the diameter of DMSi-PPO particles decreased and the number of particles increased when the amount of AMS was increased. Scanning electron micrographs of the cured epoxy resin showed that the size of crosslinked DMSi-PPO particles remained the same as before curing. It is concluded that the addition of AMS leads to an increase in the compatibility of DMSi-PPO with epoxy resin matrix and thus the G(1c) value and the adhesion properties are increased due to the increase in surface area of DMSi-PPO particles. It is also shown that the adhesion property does not depend on the curing condition because the phase structure of the epoxy resin was fixed before the curing of the epoxy resin.