This dataset contains the data used in the study examining reproductive variation along an elevational gradient in the Mediterranean lizard Psammodromus algirus in Sierra Nevada (SE Spain). The dataset includes information on reproductive phenology, maternal reproductive traits, egg characteristics, and juvenile occurrence across populations distributed along six elevational levels (300–2500 m a.s.l.). The dataset is organized into five worksheets: Phenology – Records used to estimate seasonal reproductive dynamics, including female reproductive status (gravid/non-gravid), sampling date, year, and elevation. Mothers – Individual-level reproductive data for gravid females, including body size (SVL), body mass at capture, laying date, clutch size, clutch mass, relative clutch mass (RCM), and egg-retention time. Eggs – Egg-level measurements associated with individual females, including egg mass and maternal information. Datos_Figure 6 – Records of juvenile observations across elevations and sampling dates used to characterize demographic patterns. METADATA – Description of all variables included in the dataset. Data were collected from natural populations distributed along an elevational gradient in Sierra Nevada, southeastern Spain, across multiple years. These data were used to investigate elevational variation in reproductive timing, maternal investment, offspring characteristics, and demographic structure.