Heterojunction composite structures engineered with homo-metallic elements are an effective strategy for boosting gas sensing capabilities due to their ability to effectively reduce the contact barrier for charge transfer. In this study, iso-elemental SnO/SnO₂ micro-rod composites were fabricated through hydrothermal synthesis followed by calcination. The gas sensing performance revealed that SnO/SnO₂ microstructure when calcined at 400 ℃ (referred to as M1-400), displays remarkable long-term stability, with a response value of 21.05 and the quickest recovery time of 38 s to 100 ppm of formaldehyde (HCHO) at 320 ℃, outperforming other sensors. Further investigation indicates that the enhanced sensitivity of M1-400 can be attributed to the p-n heterojunction of SnO-SnO₂ facilitating electron transport, and its increased adsorption affinity for HCHO due to higher vacuum and oxygen content. This synthesis strategy for SnO/SnO₂ suggests that this material is promising for HCHO gas sensing applications and could offer a potentially straightforward method for preparing one-dimensional metal oxides.