This paper reports the influence of surface phase transitions of a surfactant-alkane mixed adsorbed film on the foam film thickness. The DLVO free-energy between the adsorbed films is estimated using total-reflection XAFS. The foam film thickness shows discontinuous changes at the surface phase transition. In addition, the foam film thicknesses on either side of the thickness transition were in the range for common black films (CBFs), which shows a striking difference from existing thin-thick transitions between CBF and Newton black films (NBFs).