Nickel (Ni) toxicity is a crucial ecological issue that affects most soils utilized for crop cultivation. This work aimed to evaluate the effect of triacontanol (TRIA) foliar spray on photosynthesis, and physiological responses of maize (Zea mays L.) seedling under nickel stress. Ten-day-old maize seedlings grown in pots were divided into: (1) control untreated seedlings (irrigated with full nutrient solution), (2) seedlings treated with NiCl2.6 H2O (100 μM), (3) Ni-treated seedlings (100 μM) sprayed with 25 µM TRIA, (4) Ni-treated seedlings (100 μM) sprayed with 50 µM TRIA. Ni treatment reduced the growth of the 21-day-old seedlings, photosynthetic performance index (PIabs) and the contents of photosynthetic pigments, total soluble sugars (TSS), essential elements in roots, relative water content (RWC), as well as the levels of auxins and salicylic acid (SA). Nevertheless, it increased the electrolyte leakage (EL), Ni2+ uptake, plant Ni transfer rate (Nitransfer rate), root transfer rate factor (TFroot), and the contents of gibberellic acid (GA3) and abscisic acid (ABA). Both Rubisco small subunit (ZmRBCS) and abscisic acid- stress- ripening (ZmASR1) genes were up-regulated under Ni stress. TRIA foliar spray (with a preference for 50 µM) significantly improved growth attributes, PIabs, pigments content, proline content of shoots, the contents of K+, Mg2+, and Ca2+, and the expression of both ZmRBCS and ZmASR1 genes of Ni-stressed plants. TRIA also reduced membrane damage expressed as EL, Niplant uptake, and TFroot and hence alleviated the toxic effects of Ni stress. TRIA modulated the hormonal balance under Ni stress, particularly SA and auxins.