This work is aimed at investigating the influence of a plant stanol (p-sitostanol) on Langmuir monolayers from various phospholipids and comparing the effect of phytostanol versus its unsaturated analog - phytosterol (p-sitosterol). The studied phospholipids differed in the structure of polar head (phosphatidylcholine - PC, phosphatidylethanolamine - PE, phosphatidylserine - PS) as well as in the number of monounsaturated chains in PC molecule. It was found that the introduction of stanol into PC monolayers is thermodynamically favorable, contrary to its effect on PE and PS films. The magnitude of condensing and ordering effect of stanol depends both on the number of monounsaturated chains in PC molecule and on the composition of stanol-PC mixture. The analysis of BAM images evidenced phase separation of immiscible components in stanol/DPPS systems. The results of Langmuir monolayer studies for stanol/phospholipids mixtures compared with those for corresponding sterol/phospholipids systems proved quite a similar effect of both compounds on the investigated phospholipid monolayers, despite differences in the structure of tetracyclic ring skeleton. (C) 2011 Elsevier Inc. All rights reserved.