Objectives: This study focuses on the role of the mediator of smooth muscles i.e. nitric oxide in the effect of rosiglitazone on the relaxation of contractions in guinea pig trachea induced by histamine. Study Design: Experimental Study. Setting: Department of Pharmacology, Army Medical College, Rawalpindi. Period: 1st December 2018 till 14th December 2018. Material & Methods: The activity of the trachealis mucle of the guinea pigs was noted by the use of oxygenated solution of Krebs-Henseleit. The contractions were noted with rosiglitazone alone as well as in presence of an ester of L-nitro-arginine-methyl, which can antagonize the activity of NO. The activity was measured by the use of an isometric force displacement transducer and was then recorded on an oscillograph with four channels. Results: The ester L-nitro-arginine-methyl was able to reduce the relaxant effect of rosiglitazone on the contractions induced by histamine. Conclusion: It can be suggested that the relaxation induced by rosiglitazone is mediated in part through NO.