X‐ray conversion efficiencies in 351‐nm laser‐produced plasmas are investigated. X‐ray line emissions, which are useful for x‐ray shadowgraphy, have been characterized by studying dependencies on laser pulse duration, irradiation intensity, target material, and target structure. The conversion efficiencies decrease with increasing x‐ray energy and markedly decrease with increasing laser intensity. A microparticle on a plastic plate is tested in an attempt to develop a point x‐ray source. This target shows a higher conversion rate than a microwire target due to reduction in energy dissipation through hydrodynamic expansion.