In the recent years, enhanced functionality of treatment systems based on nanostructures has attracted a lot of interest. Photodynamic therapy (PDT) is one such treatment method. Here, the authors report the results of the investigations on synthesis and characterisation of gold nanoparticles (GNPs) and their application in PDT along with 5-aminolevolenic acid (5-ALA) (as photosensitiser) with no conjugation. Three sizes of GNPs were synthesised and their cytotoxicity was investigated by using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on epidermal carcinoma cell line. The results showed that the PDT efficiency of ALA increased in presence of GNPs. This effect was more considerable for 4 nm particles.