The aim of study was antiasthmatic potential of methanolic extract of leaves of Ailanthus excelsa Roxb., Simaroubaceae. Traditionally or in Indian system of medicine, A. excelsa is used in the treatment of asthma, cough, colic pain, cancer, diabetes and also used as antispasmodic, antifertility, bronchodilator. Stem bark of A. excelsa already reported for its potential against asthma. The pollens of Ailanthus excelsa reported allergic in nature and the time of collection of leaves were important in this study, generally the flowering stage of plant was avoided for the collection due to maximum chance of pollens at that time. Methanolic extract of leaves of A. excelsa was evaluated using in vitro goat tracheal chain preparation model and in vivo- Milk induced leucocytosis, eosinophilia, Clonidine induced catalepsy in mice model while Passive paw anaphylaxis and Clonidine induced mast cell degranulation in rat model. The extract showed the presence of flavonoids, terpenoids, saponins, quassonoids and test was also positive for alkaloids and steroids. The extract also showed the presence of quercetin which is flavonoid and detected on the preparative TLC plate with the help of standard quercetin. Dose response studies of methanolic extract of leaves of A. excelsa Roxb. were conducted at 100 µg mL-1 in vitro and 100, 200, 400 mg kg-1 p.o. in vivo models. The treatment with methanolic extract of A. excelsa at different dose level showed the significant (*p<0.05, **p<0.01, ***p<0.001) antiasthmatic activity. Inhibition or decrease the release of inflammatory mediators potentiates the antiasthmatic as well as antiallergic activity of methanolic extract of leaves of A. excelsa.