Atomic layer deposited Al2O3 films are incorporated into miniature light emitting diodes (mini-LEDs) as an internal moisture barrier layer. The experimental results show that the water vapor transmission rate reaches ≤10-4 g/m2/day when the Al2O3 thickness is ≥40 nm. The mini-LED with a 40 nm-thick Al2O3 layer shows negligible degradation after 1000 h of 85°C/85% relative humidity testing, whereas the device without an Al2O3 layer fails after only 500 h due to delamination occurring at the GaN surface. Current-voltage characteristics of the device without an Al2O3 moisture barrier layer indicate an increase in series resistance and ideality factor. This study provides a simple, light-weighting method to have a satisfactory encapsulation function for miniature LEDs.