Unmanned　aerial　vehicles　(UAVs),　featured　by　the　high-mobility　and　high-quality　propagation　environment,　have　shown　great　potential　in　wireless　communication　applications.　In　this　paper,　a　novel　UAV-aided　small-cell　content　caching　network　is　proposed　and　analyzed,　where　joint　transmission　(JT)　is　considered　in　the　dense　small-cell　networks　and　mobile　UAVs　are　employed　to　shorten　the　serving　distance.　The　system　performance　is　evaluated　in　terms　of　the　average　cache　hit　probability　and　the　ergodic　transmission　rate.　From　the　analytical　results,　we　find　that　(i)　the　proposed　UAV-aided　small-cell　network　shows　superior　caching　performance　and,　even　with　a　small　density　of　UAVs　the　system＇s　cache　hit　probability,　can　be　improved　significantly;　(ii)　the　content＇s　optimal　caching　probability　to　maximize　the　cache　hit　probability　is　proportional　to　the　(K+1)-th　root　of　its　request　probability,　where　K　is　the　number　of　small-cell　base　stations　that　serve　each　user　by　JT;　(iii)　caching　the　most　popular　content　in　UAVs　may　lead　to　a　low　transmission　rate　due　to　the　limited　resource　offered　by　the　low-density　UAVs.　Simulation　results　are　presented　to　validate　the　theoretical　results　and　the　performance　gain　achieved　by　the　optimal　caching　strategy.