Indium sulfide (beta-In2S3) thin films are synthesized by chemical bath deposition method using three different complexing agent volumes, triethanolamine (TEA) (0.30, 0.45, and 0.60 ml). The effect of complexing agent on the structural, morphological, optical and electrical properties of chemically deposited indium sulfide (beta-In2S3) thin films have been investigated in this work. The characterization of the present films is carried out using X-ray diffraction, scanning electron microscopy, UV-vis spectroscopy and electrical measurements. The structure of the films is polycrystalline with a cubic phase of beta-In2S3. Firstly, the band gap of the film decreases from 3.74 eV to 3.15 eV by adding 0.30 ml TEA. Then, it increases to 3.79 eV with increasing TEA. Nevertheless, previously, the refractive index of the films increases from 2.13 to 2.67 for the 0.30 mL TEA and then it decreases to the value of 2.11 with increasing TEA. Extinction coefficient, real and dielectric constant of the films are calculated using the absorption and transmittance spectra. Firstly, the electrical resistivity of the films decreases from 3.46x10(8) Omega cm to 1.33x10(7) Omega cm by adding 0.30 ml TEA. Then, it increases to the value of 2.16x10(9) Omega cm with increasing TEA. Eventually, the more conductive film with worm-like morphology detected from the scanning electron microscopy is synthesized using 0.30 ml TEA. These results show that complexing agent has an important effect on the structural, morphological, optical and electrical properties of the deposited films.