The synthesis of 3,5-dimethyl-1-prop-2-enylpyrazole was successfully carried out by reacting the 3,5- di-methyl pyrazole with 3-bromoprop-1-ene in small amount of KOH and organic solvent solid–liquid phase medium under phase transfer catalysis (PTC) and almost anhydrous conditions assisted by the ultrasonic irradiation in the 5 h at 50 8C. The main target of this carried work was to provide evidence that the reaction conditions by investigation of the kinetic behaviour, activation energy, reaction mechanism and the related parameters in the solid–liquid PTC reaction besides on to reduce time and temperature of reaction. A rational mechanism for the reaction has been derived base on the experimental result. This kinetic reaction follows pseudo first order rate law. A rate expression had developed to explain the kinetic behaviours from which the apparent rate constant (kapp) of the organic- phase reaction was obtained via investigated data. Kinetics of the reaction, including the effects of agitation speed, quantity of potassium hydroxide, quantity of water, temperature, quantity of tetraoctylammonium bromide (TOAB), volume of cyclohexanone, quarternary ammonium salts and organic solvents on the conversion of RBr and the apparent rate constant (kapp) were investigated in full length. Rational explanations for the resulting phenomena are also provided.