Knowledge about the changes in optical properties is needed for planning safer and more accurate laser treatments. A monitoring system was developed to study how the optical properties of a lipid emulsion are affected by temperature changes. A double-integrating-sphere system is modified with a controlled heating apparatus to measure the temperature-dependent diffuse reflectance and total transmittance values. The absorption and reduced scattering coefficients were estimated from the reflectance and transmittance values using an inverse adding-doubling method. The total transmittance showed positive correlation with temperature while the diffuse reflectance was found to be negatively correlated. Although the absorption coefficient did not demonstrate a statistically significant change with temperature, the reduced scattering coefficient was negatively correlated. By using the obtained optical properties, Monte Carlo simulations were performed to observe the difference in light propagation within a tissue. The results indicate that temperature-dependent changes in optical properties should be taken into consideration for a safer laser treatment.