The Absorption of incident wave can induce a variety of transitions amongst bands and sub bands that leads to the appearance of absorption peaks in the absorption spectra. UV absorption spectroscopy helps to investigate the optical properties of Nano sized particles such as LaCoO3, Fe doped LaCoO3 and Mn doped LaCoO3. For pure LaCoO3 nanoparticle, 207.49nm was the highest absorbance and there is a sudden decrease in absorbance at 245.67nm. While adding the Fe and Mn dopant into LaCoO3, the absorbance increases. For Fe doped LaCoO3 the highest absorbance is at 345.88nm and for Mn doped LaCoO3 has absorbance at 209.68nm. For pure LaCoO3 the band gap is 2.582. By adding dopant Fe into LaCoO3, the band gap decreases into 1.755 and for Mn doped LaCoO3, the band gap is 1.904. Band gap decreases due to the increase in the particle size. Hence, it is useful material for solar cell applications.