Abstract: A troffer mounting system and an adapter bracket may include a first plate provided between a T-bar of a ceiling system and a troffer housing so as to be placed on the T-bar and to extend longitudinally, a second plate connected to a first side of the first plate and having a length smaller than a length of the first plate, the second plate extending upward; two parallel vertical parts or lips connected to a second side of the first plate opposite to the first side, the two lips extending upward; and a third plate connected to a side of the second plate so as to engage with a latch, wherein the two lips do not overlap with or face the second plate in a width direction. Attachment and detachment of a lighting assembly may be easy and convenient, and manufacturing costs of the adapter bracket may be reduced.