Abstract: Process for the synthesis of para-tolualdehyde (PTAL) via carbonylization of toluene with CO catalyzed by chloroaluminate (III) type of ionic liquids (ILs) was investigated. Carbonylization reaction of toluene in ILs was tested. The results indicate Al2Cl7- is the catalytic active species and the conversion of toluene increases with increasing the amount of IL used, raising reaction temperature, prolonging reaction time, or enhancing the partial pressure of CO. The ionic liquid modified by both metallic cation and Br?nsted acid can improve the activity for the reaction. Furthermore, trialkylaminium-contained ILs with B-L complex acid such as IL-T IL-E and IL-P were prepared and firstly used in the reaction. It is found that their activity are much higher than IL-I, and IL-T who has the highest activity is the best catalyst for the reaction. Under the conditions of IL/toluene(molar ratio)=2.8, PCO 3.0Mpa, 40℃, 1h, conversion of toluene can be up to 56.4%.