Stress relaxation in uniaxial extension has been studied in networks of dihydroxy‐terminated polybutadiene,cis:trans:vinyl=26:38:36,cross‐linked by triphenyl methane‐4,4′,4″‐triisocyanate and containing 9.3% by weight of unattached polybutadiene with similar microstructure, various molecular weights, and weight to number‐average molecular weight ratios of 1.15 to 1.50. Stress relaxation measurements were made also on networks containing no unattached species and on most of the various uncross‐linked linear polymers; for two of the latter, equivalent data were obtained by conversion of dynamic measurements of the complex shear modulus. The stretch ratio was usually 1.25 and the Young's relaxation modulus was calculated from the neo‐Hookean stress‐strain relaxation. For the uncross‐linked polymers, the relaxation modulusE11(t)corresponded to a rather narrow distribution of relaxation times whose magnitudes were approximately proportional to the 3.2 power of viscosity‐average molecular weight. The contribution of the unattached species in the networks,E1(t),was calculated by difference; after multiplication by(1−v22)−1,wherev2is the volume fraction of the network component, it was compared withE11(t).The relaxation in the network appeared to be slower and more gradual to an extent which was correlated with molecular weight distribution.