This is an original study on the effect of a polyisobutylene ? polydimethylsiloxane (PIB-PDMS) block copolymer modifier used as an interfacial active agent on the dynamic behaviour of single Newtonian drops suspended in a polyisobutylene (PIB) Newtonian matrix. The results are divided in two sections. The first part includes experiments carried out on the non-modified and 2% block copolymer modified polydimethylsiloxane (PDMS) drops of five different MWs suspended in PIB920 matrix. In the second part, the effect of various concentrations of the block copolymer (0.5, 2 and 10 wt%, drop based) is studied on the drop dynamics.