Alzheimer’s disease (AD) is a progressive neurodegenerative disorder in central nervous system. The diagnosis of AD is mainly based on pathological examination after death, which shows no value to the treatment of AD. If identified and intervened as early as possible at presymptomatic states, the progression of the disease may be delayed. With the progress of positron emission tomography (PET) imaging in clinic, the diagnosis of AD at the early stage with noninvasive techniques become possible. Extracellular senile plaques (SPs), made of accumulations of β-amyloid (Aβ), is one of the most important neuropathological hallmarks of AD. Aβ targeting PET imaging agents are of great significance to early diagnosis of AD, and are one research focus in this field. The research progress of Aβ imaging agents with a small organic molecule is reviewed, which include several kinds: congo red derivatives, aminonaphtyl derivatives, benzothiazole derivatives, benzothiazole-analogues derivatives, stilbene derivatives, substituted-stilbene derivatives and other derivatives. The ideal characteristics of Aβ imaging agents are summarized, and the trend for developing Aβ imaging agents is discussed.