A novel methodology for in situ cross-linking of polymeric fibers during electrospinning is described. The electrospinning apparatus was modified to facilitate UV irradiation of the electrospun fibers while in flight to the collector target. Three polymers with different mol % of the photoreactive cinnamate functional group (4, 9, and 13 mol %) were synthesized and utilized for this study. Fibers of cinnamate functionalized poly(methyl methacrylate-co-2-hydroxyethyl acrylate) were cross-linked in situ by UV irradiation during electrospinning. Subsequent FTIR measurements on irradiated and non-irradiated electrospun fibers indicated both [2pi + 2pi] cycloaddition of the vinylene C=C and trans-cis photoisomerization of the cinnamate group. Furthermore, the irradiated copolymers were observed to form insoluble gels which indicated that the photodimerization was the primary photoprocess during UV irradiation, leading to the formation of a cross-linked network. As expected, it was found that the gel fraction increased with increasing mol % of the cinnamate species.