In recent years, an increase in the input of lanthanides (Ln), an important group of heavy metals (HMs), has been observed in the environment throughout the world (in particular soil). Anthropogenic Ln sources are mainly connected to phosphogypsum, Ln-bearing microfertilizer and micronutrients, and mine waste. Therefore, assessment of the hazards associated with the presence of Ln in the soil is an urgent issue. Hazardousness, depending strongly upon the buffer capacity of a specified soil, is determined by the organic matter content, the pH value and other soil properties. For a standard soil (containing 10% organic matter and 25% clay), the discrepancy of the hazardousness of HMs can be estimated based on the maximum permissible concentration (MPC) values proposed by ecologists in the Netherlands. Low levels of Ln contamination in the soil are found, making it possible to classify them in the group of moderately and weakly acting pollutants. The MPC value proposed for cerium (Ce) in the standard soil is 44 mg kg−1. Approximate MPC values for several other lanthanides (Ln, Pr, Nd, Sm, Gd and Dy) in soils were proposed based on MPC values for freshwater sediments in the Netherlands. According to the MPC value, Ln falls into the group of moderate- and low-hazardous heavy metals.