The high pedestal temperature H-mode experiment at JET gave a good opportunity to study the effect of a single ELM on the particle transport, because these H-mode plasmas are characterized by a long ELM free period after the L to H transition and the 2nd ELM occurs several 100ms later. It is apparent from figure 1 that in all of these pulses the ne and the Zeff increase slowly in time before the first ELM and significant increase of the ne and Zeff at the time of the 1st ELM. At the first sight this contradicts the previous experimental observation that ELMs remove impurities from the plasma core. Then what is the difference between these high pedestal H-mode plasmas and the typical H-mode plasmas at JET and other machines? We will try to answer this question using the 1.5D core transport code JETTO/SANCO.