Using a torsion balance immersed in water and natural rubber ring specimens cured with di‐tertiary‐butyl‐peroxide, measurements were made of the isothermal volume dilation of rubber for mean extensions &egr;=14, 33, and 51%, thus extending the results of Gee, Stern, and Treloar to lower strains. Chain molecular weightsMc=3000, 4400, 5100, and 5500 were employed. The chain molecular weights were determined by swelling in benzene, the uncertainty in each determination being about 10%. Observed fractional volume increases ranged from 3.2×10−5for &egr;=14% andMc=5500 to 14×10−5for &egr;=51% andMc=3000. Using Gee's expression for the volume dilation, but obtaining the slope of the stress‐strain curve from the statistical theory, curves were fitted to the data. The fitting process constituted a determination of Young's modulusEfor each rubber specimen. The resulting curves are in good agreement with those of Gee, Stern, and Treloar. Additional determinations ofEwere made from rough stress‐strain curves and from the swelling data, the internal agreement between the three determinations being fair.