A process for co-producing para-xylene and styrene from a feed (1) of hydrocarbons containing xylenes and ethylbenzene is described, the process comprising the following succession of steps: a step for separating the feed in a simulated moving bed in an adsorption column (6) containing beds of an adsorbent, from which an extract that is rich in para-xylene (7a) of at least 99.7% purity and at least one raffinate (7b) containing ethylbenzene, ortho-xylene, meta-xylene and a very small quantity of para-xylene is withdrawn; a step for dehydrogenating (10) the ethylbenzene contained in the raffinate (7b) to styrene; at least one step for primary separation of the stream (11) from the dehydrogenation step (10), to eliminate by-products; a step for separating the purified mixture (18) derived from the stream (11) containing styrene, unconverted ethylbenzene, meta-xylene and ortho-xylene, from which a stream (21a) that is rich in styrene of at least 99.8% purity and a stream (21b) containing unconverted ethylbenzene, meta-xylene and ortho-xylene is withdrawn; and a step for isomerising the stream (21b), the effluent being recycled to the adsorption column (6).