Visualization of internal cavitation flow in the nozzle is sometimes carried out with enlarged, transparent nozzles, in order to capture the images of cavitation bubbles with relatively high spatial resolution. However, it is unclear whether knowledge obtained from large-scale nozzles can be applied to nozzles with much smaller sizes, which provides a great impetus to study the nozzle size effects on in-nozzle cavitation and discharged liquid jet characteristics. In this study, visualization of cavitation in nozzles with various sizes was conducted to clarify the effects of nozzle size on cavitation. The visualization was carried out using x-ray phase contrast imaging (XPCI) to clearly observe individual cavitation bubbles. Furthermore, to investigate the effects of cavitation in nozzles with various sizes on the wavy interface structure of a discharged liquid jet, the discharged liquid jets were also visualized. Rectangular plain-orifice nozzles with a length-to-width ratio of 4 were used in the study. The width of the nozzles varies from 2.0, 1.0, and 0.50, to 0.25 mm. As a result of the study, we clarified the fact that a cavitation cloud is made of a number of deformed bubbles, while a sheet cavitation consists of a single cavitation film. In-nozzle cavitation bubbles follow the similarity law; that is, the diameter of incipient cavitation bubbles changes along with the change in nozzle size. Additionally, the wavy structure of the discharged liquid jet is finer at the super cavitation regime, although the finer structure is suppressed as nozzle size decreases, due to the relatively stronger surface tension force acting on the interface of the wavy liquid jet discharged from smaller nozzles.