Background To summarize the clinical, genotype and olfactory characteristic in patients with ¹¹C-Pittsburgh compound B (¹¹C-PIB)-positive cognitive impairment. Methods Twenty-seven patients with ¹¹C-PIB-positive cognitive impairment, including 19 patients with Alzheimer's disease (AD) and 8 patients with mild cognitive impairment (MCI), were recruited from January 2015 to February 2016 in Tianjin Huanhu Hospital. The clinical, genotype and olfactory profiles were retrospectively analyzed. Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and Clock Drawing Test (CDT), Neuropsychiatric Inventory (NPI), Activity of Daily Living Scale (ADL), and Hamilton Depression Scale-21 (HAMD-21) were used to evaluate cognitive function, behavioral and psychological symptoms, activities of daily living, and symptoms of depression, respectively. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to determine ApoE genotype, and T& T olfactometer was used to test threshold of detection and recognition. Results Compared with MCI patients, AD patients had lower MMSE score (P=0.000), orientation to time (P=0.031), short-term memory (P=0.021), recall (P=0.009), calculation (P=0.000), repetition (P=0.038), reading (P=0.021), writing (P=0.002), visual-spatial ability (P=0.039), MoCA score (P=0.000) and CDT score (P=0.020), and higher ADL score (P=0.000). But there was no significant difference in orientation to place, naming, comprehension, NPI score and HAMD-21 score between 2 groups (P>0.05, for all). There were no statistical differences in incidence of olfactory dysfunction, threshold of detection and recognition between 2 groups (P>0.05, for all). There were statistical differences in the incidence of olfactory disorders among different ApoE genotypes (Fisher's exact probability:P=0.000). To further evaluate the effect of ApoEε4 allele on the olfactory function, subjects were additionally dichotomized according to the presence or absence of at least one ApoEε4 allele. Comparing with the subjects without ApoEε4 allele, the olfactory function decreased significantly in those with ApoEε4 allele (0/11 vs. 12/13; Fisher's exact probability:P=0.000). Conclusions The patients with ¹¹C-PIB-positive cognitive impairment (AD and MCI) had significant olfactory disturbance, which was related to ApoEε4 allele. The assessment of clinical, genotype and olfactory characteristic was helpful in early diagnosis of AD patients.