An attempt was undertaken to elevate production of aromatic compounds through co‐upcycling of polystyrene (PS) and low‐density polyethylene (LDPE). The plastics samples were upcycled at 400 °C with catalyst H‐ZSM‐5. Compared to single plastic upcycling, co‐upcycling PS and LDPE demonstrated high advantages: lowered reaction temperature (390 °C), medium reaction rate (−1.35 %/°C), low yield to coke (1.62 % or less) and enhanced aromatics yield (42.9–43.5 %). In‐situ FTIR results demonstrated a constant production of aromatics in the 1 : 1 mixed plastic while in pure plastics, aromatic production quickly dropped. Compared to single PS upcycling, co‐upcycling PS with PE produced more monocyclic aromatic hydrocarbons (MAHs) at close to 43.0 % versus 32.5 % and less polycyclic aromatic hydrocarbons (PAHs) at 16.8–34.6 % versus 49.5 %. From these data, the synergy between PS and LDPE were confirmed and the mechanism in which they increased MAHs production was proposed. [ABSTRACT FROM AUTHOR]