<p>The primary objective of this work is to investigate the impact of trade openness on economic growth and to explore the nature of the relationship between the two within the member countries of the Arab Maghreb Union (AMU), specifically Algeria, Morocco, Mauritania, Libya, and Tunisia. To achieve this, we employ a Panel Smooth Transition Auto Regression (PSTAR) threshold model based on panel data with an autoregressive structure estimated over the period from 1980 to 2020. Focusing on the existence of a threshold effect, the results from our empirical investigation led us to assert that trade openness exerts a significant positive impact on economic growth within the AMU countries, specifically when trade openness is below its threshold value of 4.288%, low external investment results in a 0.018% reduction in economic growth. In contrast, growth of around 0.55% is observed when trade openness exceeds its threshold value. These findings suggest that trade liberalization can foster economic growth, but its effects depend critically on surpassing certain thresholds. Policymakers should consider the level of trade openness when formulating economic strategies to maximize the potential for long-term growth.</p>