Abstract: Ionospheric scintillation leads to rapid and random variations in signal amplitude and phase, thereby increasing positioning errors and significantly affecting GNSS positioning accuracy. This study investigates the performance of precise point positioning (PPP) under ionospheric scintillation conditions in Hong Kong, China during May 2024. A comparative analysis was conducted between single BeiDou Satellite Navigation System (BDS) (PPP-C) and dual-system (GPS+BDS) PPP (PPP-GC) in terms of positioning accuracy on scintillation and non-scintillation days. Using data from Hong Kong CORS stations, ionospheric scintillation events were detected based on the rate of total electron content index (ROTI), with May 9th selected as a scintillation day and May 26th as a non-scintillation day, both devoid of geomagnetic activity. Results indicate that ionospheric scintillation significantly degrades PPP positioning accuracy, particularly in the up direction. Although the impact of scintillation is spatially limited, the affected satellite signals can introduce errors, leading to higher dual-system PPP errors compared to single-system PPP, likely due to scintillation effects on the ionospheric piercing points of satellites. Furthermore, on non-scintillation days, dual-system PPP demonstrated superior convergence time and positioning stability over the single-system. The findings highlight that ionospheric scintillation is a critical factor influencing PPP positioning accuracy, underscoring the need for strategies to mitigate its adverse effects on positioning services.