Abstract The gold decorated SiO2@polyaniline (PANI) core–shell microspheres (GDSP) were synthesized by using silica spheres as core, polyaniline as shell, and HAuCl4 as oxidizing agent. Morphology, electroactivity, and conductivity of GDSP can be controlled by varying the HAuCl4 concentration. By increasing the concentration of HAuCl4, a large quantity of GDSP with raspberry-like morphology was fabricated. TEM images indicated that the resulting core–shell microspheres were composed of a SiO2 core with an average diameter of 800 nm and a polyaniline shell with an average thickness of 200 nm. It was also found that the electrical conductivity of the GDSP was more than 6-fold higher than that of the SiO2@PANI core–shell microspheres (SP) using ammonium persulfate (APS) as oxidizing agent. The electrochemical behavior and electro-catalytic activity of GDSP modified carbon paste electrode (CPE) was characterized by cyclic voltammetry. The GDSP modified CPE is shown to be a better surface for the electrooxidation of ascorbic acid (AA) than SP modified CPE in phosphate buffer solution of pH 7. The anodic peak potential of AA shifts obviously from 610 mV at bare CPE to 380 mV at the GDSP-modified CPE with greatly enhanced current response. Amperometry was carried out to determine the concentration of AA at 400 mV, and a good linear concentration range from 0.15 to 8 mM was found.