In this study, we used the pulsed laser ablation technique in liquid (PLAL) with varying ablation times to successfully synthesize copper iron sulfide (CuFeS2) nanoparticles (NPs) in different sizes. Transmission electron microscopy (TEM) data reveals that CuFeS2 NPs exhibit a spherical structure, with an average size of 17.9, 35.2, and 44.2 nm for ablation times of 15, 30, and 45 minutes, respectively. We employed mapping and energy disperse x-ray (EDX) to display the distribution and percentage of each element in the sample.The bonds between elements were confirmed using Fourier transform infrared (FTIR) studies. The molecular structure as well as the molecule's geometry and even symmetry can be determined using Raman spectroscopy. According to the UV-Vis spectrum, the absorption peaks of CuFeS2 NPs move to the right as the ablation time increases. As the particle size was grown, the associated band gap energy dropped from 2.68 eV to 2.11 eV. We developed a photoacoustic method (PA) to evaluate the thermophysical parameters of CuFeS2 nanofluid. Thermal effusivity (e), thermal diffusivity (α), and thermal conductivity (k) were obtained for the different samples using the closed-cell PA technique. The thermal conductivity of the samples increases from 0.636 to 0.9623 W/mK with the increase in the particle size from 17.9 nm to 44.2 nm.