In this study, a modified L-box apparatus was developed for testing the segregation resistance of self-compacting concrete (SCC). Extensive test programmes of concrete mixes were conducted using a modified L-box to determine segregation coefficient (SC) of SCC. The concrete mixes contained Portland cement replaced by different amounts of limestone powder, silica fume and fly ash, and they had different slump flow values. The SC was obtained by analysis of variance of the volumetric ratio of coarse aggregate to concrete in the sample and original mixture. The test results show that the developed apparatus and method are useful for a rapid assessment of the segregation resistance of SCC exposed to obstacles or confined flows.