"It means it's in our area, not an imported disease," Dr. Vincent Conte, deputy director of epidemiology and disease control for the Health Department, told The Miami Herald Wednesday.
The first locally acquired case was confirmed in March, the second this month.
Authorities said both patients have fully recovered.
Most cases occur in people who have traveled to infected areas, but the two locally acquired cases were in people who had not traveled, Conte said.
Dengue fever is a viral disease transmitted by mosquitoes, with symptoms including fever, severe headache, muscle, joint or bone pain, rash, nausea and vomiting.
Dengue cannot be spread directly from person to person but via infected mosquitoes, officials said, urging Miami-Dade residents to drain all standing water and use mosquito repellents.