Asthma is a global health problem. Asthma attacks are becoming more severe and more resistant to usual treatment by β₂ agonists nebulisation. The search for a new product that could reduce the morbidity of asthmatic disease seems necessary. The objective of this study was to compare the effectiveness of inhaled magnesium fluoride (MgF₂) with that of magnesium sulphate (MgSO₄) 15% alone and sodium fluoride (NaF) 0.5 M alone in rats pre-contracted by methacholine (MeCh). Fifty six adult male Wistar rats of medium weight 259 ± 15 g were divided randomly into five groups. They inhaled respectively: MeCh, MgF₂ + NaCl 0.9%, MgF₂ + acetic acid, MgSO₄ 15% single and NaF (0.5 M) single. Airway resistances were measured after each dose of MeCh by pneumomultitest equipment. Results indicated that (1) MgF₂ + NaCl 0.9%, MgF₂ + acetic acid and MgSO₄ reversed significantly the methacholine-induced bronchial constriction in rats and had a bronchodilating effect at the moment of its administration (2) MgF₂ + acetic acid led to a greater decrease (P<0.05) of bronchial resistances when compared to that obtained from MgF₂ + NaCl 0.9%, NaF exclusively and MgSO₄ alone (3) inhaled NaF alone led to a significant bronchorelaxing effect (P<0.05) that starts at the sixth dose of MeCh (17 mg/L). As a matter of fact, MgF₂ dissolved in acetic acid and delivered in aerosol form reduces significantly bronchial spasm. In conclusion, MgF₂ can be used as a bronchodilator for diseases with bronchospasma such as asthma and chronic obstructive pulmonary disease (COPD).