Cytochrome c is a highly conserved protein that is found in many multicellular and unicellular organisms. Cytochrome c is a critical intermediate in apoptosis: a controlled form of cell death that kills cells as part of their natural process of development and in response to environmental condition. To detect whether cytochrome c of the mosquito Aedes aegypti (L.) (AeaCytC) is developmentally regulated, we used quantitative real-time polymerase chain reaction (PCR) to examine AeaCytC gene expression levels in different developmental stages of Ae. aegypti. Quantitative real-time PCR showed that AeaCytC was expressed in each developmental stage, at different points in time, and it was highly expressed in teneral female Ae. aegypti. Ae. aegypti cytochrome c protein (AeaCYTC) was detected only in adult mosquitoes, not in early developmental stages of Ae. aegypti. We also investigated the effect of certain environmental factors (e.g., temperature, UV-light, and permethrin insecticide) on AeaCytC gene and AeaCYTC protein expression in adult mosquitoes, and we found that response varied with age. These results suggest that AeaCytC gene and AeaCYTC protein play functional roles in the development of Ae. aegypti and the differential expression of cytochrome c has potential as a biomarker for environmental and chemical stress.