A mobile drilling rig (1) includes a mast (3), a drilling head (5) for sliding in use along the mast (3), and at least one hoist (4). The drilling head (5) is supported by at least two hoisting wire cables (24). The mast (3) is telescopic and includes a main load carrying member (31), for extending the telescopic mast (3), at whose end a plurality of pulleys (26) are provided, on which the hoisting wire cables (24) slide. The main load carrying member (31) is adapted to bring the mast (3) from a closed operating configuration to an extended operating configuration and vice versa. The movement of the drilling head (5), when the mast (3) is in the extended operating configuration, takes place by the hoisting wire cables (24), which are pulled and released by the at least one hoist (4).