The photochemical behaviour of spontaneously formed microemulsions obtained upon dilution of ethanolic solutions of trans-anethole (E-1-(4-methoxyphenyl)propene, t-A) with water is compared to that of homogeneous ethanolic t-A solutions. Significant differences in reactivity reflect the confined nature of the aggregated t-A which leads to reduced yields of isomerization and dimerization products. In contrast to homogeneous solutions, where a photostationary state enriched in the Z-isomer (c-A) is rapidly reached, the proportion of c-A formed upon irradiation of t-A microemulsions remains below 15%. In the presence of oxygen the formation of trans-anethole oxide is observed which, when formed in non-homogeneous environments, undergoes polymerization.