A foldable frame includes first and second mounting assemblies pivotally connected to each other and rotatable with respect to each other between a folded position and an unfolded position. A foldable frame also includes one or more retainers. A retainer has a first coupler and a second coupler, with one disposed at the first mounting assembly and the other at the second mounting assembly. When the first and second mounting assemblies are in the folded position, the first and second couplers of each retainer engage with each other, and thus retain the first and second mounting assemblies in the folded position and prevent the foldable frame from accidental unfolding.