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Foliar molybdenum (Mo) application may enhance the nitrogen (N) acquisition by the plants and increase the yield and quality of vegetables. A study was conducted to investigate the effect of foliar Mo spray on N nutrition and yield of crispleaf lettuce (Lactuca sativa L., cv. Grand Rapids) grown in the spring-summer period. The experiment was carried out at Ourinhos, São Paulo State, Brazil, from October 2013 to January 2014. Treatments consisted of five Mo rates [0 (control), 25, 50, 75, and 100 g ha-1 of Mo] divided into two foliar sprays, at 14 and 21 days after planting. Foliar application of Mo rates reduced the nitrate (NO3 -) concentration, and increased the concentrations of ammonium (NH4 +), total N and Mo in the lettuce leaves. These data indicate that the foliar Mo application improved N assimilation of lettuce plants, resulting in less accumulation of NO3 - in the leaves and therefore, improving the quality of the vegetable. Number of leaves per plant was not affected by the foliar Mo application. The 55 to 62 g ha-1 of Mo application resulted in increased of the leaves fresh weight (33%), leaves dry weight (28%) and commercial yield (34%) of crisphead lettuce, respectively. Results suggest that Mo deficiency can compromise the N metabolism of plants, and result in lower commercial yield of crispleaf lettuce. [ABSTRACT FROM AUTHOR]