The first-order phase transitions in adsorbed monolayers of 2-hydroxyethyl laurate have been studied by film balance and Brewster angle microscopy (BAM). A cusp point in the surface pressure-time (pi-t) curves indicates the commencemnet of phase transition. The critical surface pressure necessary for the phase transition increases with increasing temperature. Large size circular domains having characterishtic internal stripes are observed up to 10 degrees C. The width of the stripes increases with increasing termperature. The separate stripes in a domain undergo continuous narrowing into a core defect which lies on the domain peripheral line at 2 degrees C. The core defect seems to be also present at higher temperatures but remains far out of the doman boundary at 10 degrees C. Two surface phases observed after the cusp points by BAM are pseudo equilibrium state and the global equilibrium is attained with the formation of one condensed surface phase after a long time.