Background and Aim: Determination of the age of vector mosquitoes is of particular importance in epidemiological studies of diseases transmitted by them, such as viral and parasitic diseases. The objective of this study was to determine the daily age of Anopheles stephensi based on changes in pteridine concentration in female mosquito cuticles by liquid chromatography (HPLC).Methods and Materials: Females of Anopheles stephensi were raised in an insectary (28oC, 70% relative humidity). At 1, 5, 10, 15, 25, 30 days post-emergence they were divided into groups of 10 mosquitoes each. The mosquitoes in each age group were further divided into 3 subgroups of 10 each for chromatographic (HPLC, emotion = 355 nm and excitation= 465 nm) pteridine extraction. The chromatograms obtained were compared with the respective standards to determine the types of pteridines.Results: Four types of pteridines were detected in the cuticle of Anopheles stephensi, including isoxanthopteridine, pteridine-6-carboxylic acid, biopteridine, and xanthopteridine. They were all present in all the cuticle of the mosquitoes; however, no biopteridine in the head or xanthopteridine in the thorax were found. Generally, as the age of the mosquitoes increased, pteridine concentrations kept declining, such that after 30 days the total concentration reached 10% of the original.Conclusion: The findings indicate that there is a negative correlation between the concentration of pteridines in the cuticle and daily age of female mosquitoes. The method described can be used as a standard method to determine the daily age of Anopheles, as well as of other mosquito species, since it is fast and precise and needs small samples. Its major limitation is non-availability of HPLC in many parts of the country, although it is possible to freeze dead mosquitoes and transfer them to centers where HPLC is available.