Photothermal therapy is a minimally invasive anticancer therapy, where the energy of light irradiation is converted by photothermal agents to heat energy, thus increasing the temperature in the cancer cells. The efficiency of this therapy depends on the used photosensitizer, which must have several design criteria, such as plasmon resonance tenability and conversion efficiency. Based on these criteria, gold nanodahlias (AuD NPs) were synthesized and their anticancer properties were determined under irradiation with lasers operating at three different electromagnetic wavelengths (405 nm, 650 nm and 808 nm) of two colon cancer cell lines SW480 and SW620. Scanning and transmission electron microscopies revealed that the size of the synthesized AuD NPs is around 70 nm, while their UV-Vis spectrum showed a maximum absorbance value at 625 nm wavelength. The MTS assay showed that for 625 nm laser irradiation in the presence of NPs, the mortality of the two lines of cancer cells is around 70%, in comparison with control samples (untreated cancer cells). Fourier-transform infrared and Raman spectroscopy showed that the most visible chemical changes, especially in DNA, RNA, phospholipids, lipids and proteins functional groups, occur in the colon cancer cells cultured with AuD NPs irradiated with 650 nm and 808 nm lasers. A photothermal conversion efficiency reaching 50% is observed for AuD NPs irradiated with 650 nm and 808 nm wavelengths. All of these properties of AuD NPs suggest that these nanoparticles could be effective potential nanophotosensitizers in photothermal anticancer therapy.