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The <i>Cupressaceae</i> family includes species considered to be medicinal. Their essential oil is used for headaches, colds, cough, and bronchitis. Cedar trees like <i>Chamaecyparis lawsoniana</i> (<i>C. lawsoniana</i>) are commonly found in urban areas. We investigated whether <i>C. lawsoniana</i> exerts some of its effects by modifying airway smooth muscle (ASM) contractility. The leaves of <i>C. lawsoniana</i> (363 g) were pulverized mechanically, and extracts were obtained by successive maceration 1:10 (<i>w</i>:<i>w</i>) with methanol/CHCl₃. Guinea pig tracheal rings were contracted with KCl, tetraethylammonium (TEA), histamine (HIS), or carbachol (Cch) in organ baths. In the Cch experiments, tissues were pre-incubated with D-600, an antagonist of L-type voltage-dependent Ca²⁺ channels (L-VDCC) before the addition of <i>C. lawsoniana</i>. Interestingly, at different concentrations, <i>C. lawsoniana</i> diminished the tracheal contractions induced by KCl, TEA, HIS, and Cch. In ASM cells, <i>C. lawsoniana</i> significantly diminished L-type Ca²⁺ currents. ASM cells stimulated with Cch produced a transient Ca²⁺ peak followed by a sustained plateau maintained by L-VDCC and store-operated Ca²⁺ channels (SOCC). <i>C. lawsoniana</i> almost abolished this last response. These results show that <i>C. lawsoniana</i>, and its active metabolite quercetin, relax the ASM by inhibiting the L-VDCC and SOCC; further studies must be performed to obtain the complete set of metabolites of the extract and study at length their pharmacological properties.