Early diagnosis and treatment of AD are critical for delaying its progression. The present study, therefore, examined the cognitive status and neuropathological characteristics of 4-month-old 5X familial AD (5XFAD) transgenic (Tg) mice, as an early stage of AD animal model. The novel object recognition task was performed with retention tests at varying intervals (i.e., 10 min, 1 h, 4 h, and 24 h) to measure the retention capacity of recognition memory of 5XFAD mice. At the 4h retention interval, 5XFAD mice exhibited worse performances than non-Tg control mice. Therefore, using amyloid-beta (Aβ) 42- and 4G8-immunoreactive plaques, the accumulation of Aβ was examined in the gray and white matter of the system that was necessary for the retention of recognition memory, with a focus on the hippocampus and retrosplenial cortex. The expression of ionized calcium-binding adapter molecule-1 (Iba-1) was also examined to measure microglial activation. The immunohistological analysis of Aβ and Iba-1 revealed that the retrosplenial cortex was the most affected region in the brains of 4-month-old 5XFAD mice. These findings indicate that the cognitive and neuropathological characteristics of 4-month-old 5XFAD mice would provide a research platform for studying early diagnosis and treatment of AD.