Polycrystalline Bi3Se2Te thin films were grown on c-plane sapphire substrates by pulsed laser deposition (PLD) in helium atmosphere. Two different helium gas pressures of PHe =2.7×10-3 and 8.7×101 Pa were used during deposition. The microstructure, surface morphology, and nanomechanical properties of the obtained Bi3Se2Te films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation, respectively. Results indicated that the films deposited under different PHe's all exhibited highly c-axis-oriented characteristics with granular morphology. Nevertheless, the surface roughness showed strong dependence on PHe, increased from 1.3 nm to 11.8 nm for films grown at lower and higher PHe, respectively, suggesting a prominent role played by the helium gas in the nucleation and growth behavior during deposition. The Weibull statistical analysis was adopted to calculate the characteristic values of hardness and Young's modulus of the Bi3Se2Te films. In addition, the values of the fracture toughness and the nanoindentation-induced fracture behaviors of Bi3Se2Te thin films were also investigated and the results indicated that films with smaller grain size and larger surface roughness give rise to larger fracture toughness.