A bonnet mounting apparatus of an agricultural work vehicle enables a bonnet that covers an engine compartment of an agricultural work vehicle to be opened upward. The bonnet mounting apparatus includes: a fastener on which a coupling protrusion is provided, and which is attached to the inside of one end portion of a bonnet; and a hinge on which a coupling recess, into which the coupling protrusion is inserted, is provided, and which is hingedly coupled to the upper end of a bonnet support at a vehicle body side so as to be rotatable upward and downward. According to the present invention, the bonnet is easily connected to the vehicle body by inserting the coupling protrusion of the bonnet into the coupling recess of the hinge at the vehicle body side.