Abstract: A pot experiment with two representative soils (purple soil and yellow soil) in Southwest China was conducted to study the effects of applying pig manure on the lettuce (Lactuca sativa L. var. capitata L.) yield and nitrate content and the soil nutrients. Applying pig manure increased the lettuce yield significantly, and the increment was higher for yellow soil than for purple soil. The nitrate and total nitrogen, phosphorus, and potassium contents in lettuce plants were closely related to soil type and pig manure application rate. According to the evaluation standards of the nitrate pollution level of vegetables formulated by the Chinese Academy of Agricultural Sciences, the nitrate content in lettuce plants growing on purple soil was lower than the grade I (≤432 mg·kg^-1, slight pollution) in treatments CK (no pig manure application) and M₁ (applying 200 kg N·hm^-2 of pig manure), but generally higher than the grade II (≤758 mg·kg^-1, moderate pollution) while not exceeded the grade III (≤1440 mg·kg^-1, heavy pollution) in other treatments. The nitrate content in lettuce plants growing on yellow soil was lower than the grade I, except that in the treatments of chemical fertilizations and of M₈ (applying 1600 kg N·hm^-2 of pig manure) where the plant nitrate content was exceeded the grade II. The critical value of OlsenP characterizing the apparent leaching risk level of phosphorous in yellow soil and purple soil was 96.3 and 107.7 mg·kg^-1, respectively. The environmental safety capacity of pig manure was higher for yellow soil than for purple soil. Applying pig manure increased the organic carbon and total nitrogen contents of the two soils significantly.