Abstract: To develop the polysaccharides from Spirulina platensis-chitosan composite film (PSP/CH-film) with good performance, nano-SiO₂ modified SiO₂/polysaccharides from Spirulina platensis-chitosan composite film (SiO₂/PSP/CH-film) was developed. The effect of different mass concentrations and different particle diameters of nano-SiO₂ on the structure, physical properties, mechanical properties, bacteriologists and biodegradability of SiO₂/PSP/CH-film were explored. The results showed that: Nano-SiO₂ had good compatibility with chitosan and polysaccharides from Spirulina platensis, and the surface of SiO₂/PSP/CH-film was smooth and flat. The addition of nano-SiO₂ with a mass concentration of 0.05%~0.15% and the particle size of 30 nm improved the tensile strength and antibacterial properties of SiO₂/PSP/CH-film, increased the thickness, swelling degree and opacity, but it delayed the biodegradability and decreased the elongation at break. When the mass concentration of nano-SiO₂ was 0.1% and the particle size was 30 nm, the SiO₂/PSP/CH-film exhibited excellent antibacterial properties and tensile strength, which was beneficial to prolong the shelf life of food and improving the actual durability of the film. When the mass concentration of nano-SiO₂ was constant and nano-SiO₂ with a particle size of 500 nm was added, only the elongation at break increased with the increase of the particle size. Therefore, nano-SiO₂, as a good modified material, could be well dispersed in the blending system of PSP/CH-film, improved network structure and comprehensive performance of the composite film.