In this study, we investigated the influence of paclitaxel nanocrystals (PTX-NC) surface charge on cell internalization and cell cytotoxicity. PTX-NCs were prepared using the nano-precipitation method. The surface-modified PTX-NCs were prepared using an absorption method with positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS). The morphologies of the surface-modified and unmodified PTX-NCs were characterized by field emission scanning electron microscopy. An in vitro drug release study was performed in phosphate-buffered saline (pH 7.4) containing 0.5% (w/v) Tween 80 for 48h. Cell internalization was evaluated at time intervals of 0.5, 1, and 2h, and cell cytotoxicity was analyzed for 24h using A549 cells. Three different types of PTX-NCs with a mean size of around 300-400nm were successfully prepared. The zeta-potential revealed PSS-PTX-NCs (-22.7±5.1 mV), PTX-NCs (- 2.4±2.9 mV), and PAH-PTX-NCs (+ 19.3±3.4 mV). The three types of PTX-NC exhibited higher drug release than pure PTX. The positive charge on PTX-NC resulted in higher cell uptake and cell cytotoxicity than the negative charge on PTX-NC. Moreover, the positive charge on PTX-NC showed stronger interactions with bovine serum albumin. In conclusion, the positive charge on PTX-NCs improved cell internalization, cell cytotoxicity, and interactions with bovine serum albumin.