In Kato's paper on Euler system, he constructed an explicit reciprocity law to compute Bloch-Kato's dual exponential map. In this talk, we give a variant of Kato's explicit reciprocity law and show that it is compatible with Bloch-Kato's dual exponential map. As a consequence, the new map is compatible with Kato's original one. This is a joint work with Pierre Colmez.