A conductor composition being able to easily secure the conductivity at the same level as an Ag bulk at low temperature process, a mounting substrate utilizing the conductor composition and a mounting structure utilizing the conductor composition are provided. In a mounting structure, wherein one or more electrodes (11) of a mounting substrate (10) and one or more surface mounting components (20) are connected through a conductor composition (30), and one or more surface wirings (14) of the mounting substrate (10), one or more inner-layer wirings (13) and one or more via conductors (12) are formed with the conductor composition, the conductor composition contains conductive particles with electrical conductivity, and the conductive particles are composed of low crystallized Ag fillers with the crystal size of 10 nm or less.