Recent experiments on the 105 K transition in SrTiO3 by means of the high-angle double-crystal X-ray diffractometry (HADOX) are presented and discussed. The temperature dependence of the Bragg peak-width shows two anomalies: A peak in the temperature range Tc ± 2 K and a gradual increase over a range of about 10 K below Tc. The former is due to critically enhanced fluctuation and is connected with the precursor behaviour of the lattice constant. The latter is attributed to a change in mosaicity and is consistent with an anomaly in the intensity vs. temperature relation. By combining HADOX with the use of white X-rays and an energy sensitive detector, all the results mentioned above are found being common in the region with the depth from the specimen surface 1 to 57 pm, and regarded as representing bulk behaviours. © 1985 The Japan Society of Applied Physics.