An optical assembly and a camera module are provided, including a first submodule and a second submodule. The first submodule includes a first lens barrel and a first lens group disposed in the first lens barrel. The second submodule includes a second lens barrel and a second lens group disposed in the second lens barrel. The first lens group and the first lens barrel have a first major engagement mechanism and a first auxiliary engagement mechanism, respectively. The second lens group and the second lens barrel have a second major engagement mechanism and a second auxiliary engagement mechanism, respectively. The first auxiliary engagement mechanism and the second auxiliary engagement mechanism are assembled to form an auxiliary engagement section. The first major engagement mechanism and the second major engagement mechanism are assembled to form a major engagement section.