Rainfall is one of most important environmental factors influencing ecosystem structures and processes, and changes in rainfall can alter plant growth in arid/semi-arid regions. Currently, the impacts of rainfall patterns on the biogeochemical cycles of C, N, and P in terrestrial ecosystems have been well studied. However, a knowledge gap exists with regard to the changes in soil and plant stoichiometric characteristics along rainfall gradients in Mongolian pine (Pinus sylvestris var. mongolica) plantations. We selected one native Mongolian pine plantation and four plantations along a rainfall gradient in the Horqin Sandy Land. We measured stoichiometric characteristics in the soil (0-10,10-20, and 20-40 cm) and leaves (1-and 2-year old). Our results showed that:(1) Soil C, N, and P concentrations in Mongolian pine plantations in the Horqin Sandy Land were significantly lower than those in native Mongolian pine plantation; (2) Soil C, N, and P concentrations and soil C:P and N:P increased with increasing rainfall in the Horqin Sandy Land, but soil C:N decreased along the rainfall gradient; (3) Leaf C concentration decreased, and leaf N concentration and N:P increased with increasing rainfall, but there was no clear trend for leaf P concentration along a rainfall gradient; (4) there were significant positive relationships between leaf P concentration and soil C, N, and P concentrations, but not for leaf C and N. Our results implied that soil nutrients limit the growth of Mongolian pines in the Horqin Sandy Land compared with growth in native land. Furthermore, the soil N limitation decreased with increasing rainfall, but soil P limitation increased. Our results could improve the management of Mongolian pine plantations following introduction into the Horqin Sandy Land.