We present results of the RXTE observations of an extremely intense X-ray burst detected from the source 4U1724 - 307 in the globular cluster Terzan 2 .
The burst profile was complex consisting of two precursors and a long primary peak .
During the first ( strong ) precursor the source luminosity , L \sim 3.6 \times 10 ^ { 38 } \mbox { erg s } ^ { -1 } , was comparable with that measured in the main event .
The structure of the profile , its dependence on energy and observed spectral evolution indicated strong photospheric expansion of a neutron star .
The effective temperature and radius of the photosphere were estimated from the black body model at different stages of expansion , their correlations and specific features of the profile were analyzed and discussed .