Background Individuals with neurodegenerative diseases such as Parkinson disease (PD) and Alzheimer’s (AD) disease often present with perceptual impairments at an early clinical stage. Therefore, early identification and quantification of these impairments could facilitate diagnosis and early intervention. Objectives This study aimed to compare proprioceptive and olfactory sensitivities in individuals diagnosed with PD and mild cognitive impairment (MCI). Methods Proprioception in the forearm and olfactory function were measured in neurotypical older adults, individuals with PD, and individuals with MCI. Position and passive motion senses were assessed using a passive motion apparatus. The traditional Chinese version of the University of Pennsylvania smell identification test (UPSIT-TC) and the smell threshold test (STT) were used to identify and discriminate smell, respectively. Results Position sense threshold between the groups differed significantly ( p  < 0.001), with the PD ( p  < 0.001) and MCI ( p  = 0.004) groups showing significantly higher than the control group. The control group had significantly higher mean UPSIT-TC scores than the PD ( p  < 0.001) and MCI ( p  = 0.006) groups. The control group had a significantly lower mean STT threshold than the PD and MCI groups ( p  < 0.001 and p  = 0.008, respectively). UPSIT-TC scores significantly correlated with disease progression in PD (r = − 0.50, p  = 0.008) and MCI (r = 0.44, p  = 0.04). Conclusions Proprioceptive and olfactory sensitivities were reduced in individuals with PD and MCI, and these deficits were related to disease severity. These findings support previous findings indicating that perceptual loss may be a potential biomarker for diagnosing and monitoring disease progression in individuals with neurodegenerative diseases.