First-order statistical properties of ultrasonic speckles back-scattered from an interface with tiny pints on, which is considered as one kind of weak scatterin g interface, are studied in this paper. Based on four assumptions, theoretical a nalyses indicate that the amplitude of ultrasonic speckles in space is in the fo rm of Rice distribution, and the phase probability density function of the ultra sonic speckles is a compound function of Gauss distribution function and Gauss p robability integral function. When the density of the pits on the interface is v ery high, the amplitude of ultrasonic speckles becomes Rayleigh distributed. To verify the theoretical analysis conclusion, the amplitude probability distributi on of ultrasonic speckles is measured by using a set of experimental systems wit h step scanning controlled by a computer, which is built by the authors. The exp erimental results are in good agreement with the theoretical predicted results. So, the assumptions proposed in this paper are suitable for the theoretical anal yses.