Iran’s Alireza Ghaleh Naseri seized a silver medal in the men's discus F56 on Saturday.
Dos Santos, a four-time World Championships medallist, set a Paralympic record by throwing 45.33m.
Ghaleh Nasseri won the silver medal with a throw of 44.04m.
Leonardo Diaz of Cuba rounded off the podium with bronze having managed a best effort of 43.58.
Iran’s Sareh Javanmardi has won a gold medal in the women’s 10m air pistol SH1.
Saman Pakbaz has also claimed a silver medal in the men's shot put - F32.
Iran has participated at the 2016 Summer Paralympics with 111 athletes in 12 sports.
The Iranian delegation finished in 11th place in the previous edition, winning 10 gold medals, seven silvers and seven bronze medals.