Neolithic, Copper Age and modern land snail shells from the Los Castillejos archeological site (37°20′N), SE Iberian Peninsula, were analyzed for 13 C/ 12 C and 18 O/ 16 O ratios to estimate the paleoenvironmental conditions during shell deposition. Modern and ancient δ 13 C values ranged from −9.2‰ to −7.7‰ and from −13.6‰ to −5.7‰, respectively, and they differed among taxa. δ 13 C values were similar for Neolithic (δ 13 C = −8.1 ± 2.3‰), Copper Age (δ 13 C = −8.4 ± 0.6‰) and modern (δ 13 C = −8.4 ± 0.5‰) herbivorous Cernuella specimens. Alternatively, fossil shells of the herbivorous Ferussacia folliculum (δ 13 C = −9.9 ± 1.2‰) and the omnivorous Rumina decollata (δ 13 C = −11 ± 1.2‰) showed substantially lower δ 13 C values than modern specimens, which may suggest lower water stress during the early to mid Holocene than today. The δ 18 O values from modern specimens ranged from −1.1‰ to +0.6‰ while the δ 18 O values from fossil specimens ranged from −6.7‰ to +0‰ and they differed among species. Cernuella exhibited shell δ 18 O values that increased from the Neolithic (δ 18 O = −2.3 ± 1.8‰) and Copper Age (δ 18 O = −1.7 ± 0.6‰) to the present (δ 18 O = −0.3 ± 0.5‰). The δ 18 O values of fossil shells of F. folliculum (δ 18 O = −3.7 ± 1.0‰) and R. decollata (δ 18 O = −4.0 ± 1.6‰) were also lower than modern shells. Calculations of a published snail-flux balance mixing model for δ 18 O values indicate that early to mid Holocene shells precipitated during times when relative humidity was greater than today. The SE Iberian Peninsula was noticeably wetter ∼7200 cal BP, and experienced drier conditions thereafter. The results are consistent with other regional paleoclimatic proxies and reinforce the potential use of land snail shells as paleoenvironmental archives.