One of the widely used techniques for producing recombinant adeno-associated virus serotype 2 (rAAV2) particles, as viral vectors for gene therapy applications, is the triple transient (TT) transfection of human embryonic kidney 293 (HEK293) cells. It is desirable to optimize this transfection process for more efficient manufacturing of rAAV viral vectors for gene therapy purposes. We examined the application of dimethyl sulfoxide (DMSO) as an additive to this transfection technique to improve the expression yield of rAAV2 particles with HEK293 cells in adherent and suspension cell culture modalities. This assistance by DMSO should increase the trafficking of plasmid DNA (pDNA) through the cell membrane, and thus, increase the viral titer of rAAV2 full capsids at the time of harvesting the cell culture. The study demonstrated that DMSO as an additive for the TT transfection process led to an 8.2-fold increase in the expression yield of full AAV2 capsids using HEK293 cells in adherent cell culture modality, and also led to a 4.0-fold increase in the expression yield of full AAV2 capsids using HEK293 cells in suspension cell culture modality. There are no reported studies on the application of DMSO as an additive to the TT transfection process of HEK293 cells for the production of AAV particles. This is a novel, simple, and inexpensive method to improve the yield of rAAV2 full capsids with the TT transfection process of HEK293 cells, using a well-known cryoprotectant agent (CPA), as an additive to this transfection process.