Background: Risperidone (RPD) has been indicated for oral administration twice a day in the commercial products. However, multiple daily doses of antipsychotic medication lead to a failure of treatment due to poor patient compliance.  Objective: The aim of this study was to develop modified release formulations using a nanocomplex prepared by electrostatic interactions between cationic RPD and anionic dextran sulphate (DS). Material and Method: To prepare the nanocomplex, the DS solution was added to the RPD solution simultaneously with the ultrasonic dispersion. The complexes were prepared according to the various ratios of DS to RPD and pH conditions (pH 1.0 - pH 5.0).  For the physicochemical characterization, the nanocomplex was investigated in terms of encapsulation efficiency, mean particle size, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and in vitro dissolution. Results: Optimized nanocomplex (RPD/DEX = 1/1 (w/w), pH 3.0) showed the encapsulation efficiency of over 80%. The mean particle size was 284.5 ± 9.8 nm. The results of the DSC analysis confirmed that intrinsic melting peak from RPD disappeared and changed to the amorphous form in the nanocomplex. In the FT-IR spectra, the peak of piperazine and sulfate from RPD and DS, respectively, changed due to the electrostatic interaction. In the dissolution test, the nanocomplex gave a modified release curve with immediate release (66.21 ± 0.44% at 15min) and following sustainable release (97.24 ± 0.83% at 12h). Conclusion: Our results demonstrate that the nanocomplex developed by electrostatic interactions of RPD - DS is a promising modified release formulation.