Background: Shwas kuthar rasa is a prestigious and potential herbomineral formulation of Ayurveda tested on 100 years of time scale for the treatment of asthma, allergy, and other respiratory problems. However, there is a lack of scientific work on Shwas kuthar rasa. Objective: To prepare and physicochemically evaluate mercury-based Shwas kuthar rasa herbomineral formulation of Ayurveda for asthma and allergy. Materials and Methods: Shwas kuthar rasa was prepared as per Ayurvedic text and characterized by various modern analytical techniques, viz., transmission electron microscopy (TEM), X-ray diffraction (XRD), far infrared (IR) spectroscopy, fourier transform IR spectroscopy, energy dispersive X-ray analysis, and inductively coupled plasma-mass spectroscopy. Results: Study clearly revealed that prepared Shwas kuthar rasa formulation shows several crystallites agglomerate into a single particle. It yields submicron size particle structure (1.22 μ) with TEM analysis. The usage of mercury in the formulation found in the form of mercuric sulfide (HgS) and reaching to nanocrystalline (31-56 nm) size by XRD analysis. Conclusion: The present study indicates Shwas kuthar rasa is nanocrystallite with submicron size particle. Trituration of Kajjali helps in the formation of HgS and increases the crystallinity in the formulation.