The value of the effective delayed neutron fraction has been measured for a compact loading of the BSR-I by the boron-substitution technique. The value obtained was 0.0080 ± 0.0002. By adopting the value of the true delayed neutron fraction. β = 0.0064 ± 0.0002, measured by Keepin et al., the ratio of the effective delayed-neutron fraction to the true delayed-neutron fraction is found to be 1.25 ± 0.05. When this quantity was computed by a three-group PDQ-code calculation, the result was 1.25, an agreement which suggests the validity of the computational method.