La1-x Sr (x) FeO3 (x = 0.0-1.0) nanoparticles have been synthesized by a sol-gel method. The samples are characterized by thermogravimetric/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The La1-x Sr (x) FeO3 (x = 0.0-1.0) materials have been sintered at 650 A degrees C. Both the structural properties and phase transitions with increasing strontium content in La1-x Sr (x) FeO3 are presented by analysis of XRD data. Formaldehyde gas-sensing properties of La1-x Sr (x) FeO3 have been investigated. The experimental results show that the optimum operating temperatures of La1-x Sr (x) FeO3 varies with Sr content of x. Among all the samples, La0.7Sr0.3FeO3 shows a maximum response to formaldehyde. Finally, the formaldehyde gas-sensing mechanism has been presented.