The grooved carpet shell clam (Ruditapes decussatus) is one of the most economicallyimportant mollusks inhabiting Mediterranean lagoons and sandy beaches both from fisheries and aquaculture. The present study aims to study the impact of different levels of acidification on this calcifying organism.  Juvenile clams (avg. Shell Length, SL= 23.22 ± 0.84 mm) were incubated in CO₂ enriched seawater at four different CO₂ concentrations [420 ppm (ambient control), 550 ppm, 750 ppm and 1050 ppm] representing projected atmospheric CO₂ concentration scenarios for the year 2100 by IPCC. The studied biological parameters showed slight decrease with increasing pCO₂. However, differences were not significant. Standard length decreased as pCO₂ concentration increased, with a maximum average decrease of (-0.12) recorded at 750 ppm as compared to the control group. Regarding total weight, the decrease was highest (-0.10) in both 550 and 1050 ppm.  Moreover, clams kept at 550 ppm showed the lowest condition index (11.40 ± 1.49) and highest mortality rate of 8%. The study of physiological response showed increase in metabolic rate and ammonia excretion in both 550 ppm and the control 420 ppm groups. Algal feed clearance rate decreased with increasing acidification with highest value in the control (420 ppm) group and lowest average value of 3.34 l/h^-1in the extremely high pCO₂ (1050 ppm) group. By the end of century, ocean acidification may exert additional stress on the health of R. decussatus and its economic value.