To improve the transparency, flexibility, and solubility of polyimide, and to fabricate a negative working photoresist, polyamic acid, polyurea, and poly(amic acid-co-urea) in various contents were synthesized. Photosensitive diazoresin was synthesized and was used as the photocrosslinking agent. Characteristics of the polymers were identified by using IR, EA, DSC, TGA, and UV. From dissolution capabilities and thermal properties of the polymers, we chose the most suitable polymer PA25 as the main resin of the negative photoresist. The mixture of the polymer and diazo resin can be used as a negative photoresist. Optical characteristics of the polymer and diazo resin were evaluated by UV spectrophotometer. It was found that the polymer and diazo resin showed different absorption wavelengths under UV exposure. Characteristics of the negative photoresist were investigated by using i-line lithography. A contact printing exposure technique was used in this investigation. Dissolution rate and resolution capability of the photoresist containing various amounts of diazo resin were evaluated. The optimal prebaking time, postbaking time, and SEM patterns of the negative photoresist were also investigated.