The sol-gel technique (dipping method) was used because it is simple, economic and does not require complicated equipment. The cobalt chloride salt was used as a source of cobalt ions. The effect of : deposition time (15, 30, 45 and 60 sec), pH value (9.5, 10.5, 11.5 and 12.5) and annealing temperature (300, 400, 500 and 600 °C) on the properties of Co3O4 thin film was study by used X-Ray diffraction and EDS for structural properties, optical microscope (OM), SEM and AFM for morphological properties, UV-VIS for optical properties, Hall Effect for electrical properties, Magnetic susceptibility balance for magnetic properties and gas sensitivity test for measured the sensing properties. X-Ray diffraction result has confirmed the formation of cubic spinal Co3O4. And the films crystallinity increase with increase the deposition time and annealing temperatures while pH value have different effect. The OM and SEM revealed to formation of smooth surface and the growth increase with the deposition time and annealing temperatures. AFM shows the pH value have different effect on the grain size of the films. The transmission was decrease with increase the deposition time (from 15 to 60 sec) and annealing temperatures (from 300 to 600 °C) due to increase the thickness and the improvement in films crystallinity respectively. Co3O4 found have high absorption coefficient more than 105 cm-1. The energy band gap found to be increases with increase the film thickness from (2 to 2.42 eV) while decrease with increase the annealing temperatures from (2.5 to 2 eV) because of improvement in films structure. The Hall effect measurement shows that the Co3O4 all samples are p-type conductivity and the carrier concentration and films conductivity was increase with increase the deposition time (from 15 to 60 sec) ( from 1.85 to 3.84 *1017 cm-3) and ( from 1.03 to 1.47 *10-5 Ω-1 cm-1 ) respectively, and annealing temperatures (from 300 to 600 °C) ( from 3.9 to 9.8 *1017 cm-3) and ( from 0.2 to 2 *10-4 Ω-1 cm-1) respectively, while the pH have different effect. Co3O4 thin film found to be antiferromagnetic material and their susceptibility increase with increase the pH value and decrease with increase the annealing temperatures the maximum observed susceptibility at pH 11.5 equal to 12917*10-6 cm3/mole which higher for about twice from the standard value. Co3O4 was found to be sensitive NO2 gas and it's sensitivity improved by increase the deposition time (from 35 to 53 %) and annealing temperature (from 50 to 73%) and slightly with pH value (from 42 to 53 %).