To provide a method of controlling the manufacture of a seamless tube by which the occurrence of defective products caused by mandrel mill rolling is prevented and the seamless tube excellent in surface properties is manufactured easily.

The seamless tube is manufactured by heating a hollow tube stock 9, further, reheating a tube stock for stretch reduction which is charged and stretch-reduced in the state where a mandrel bar 10 is inserted into a mandrel mill in which a plurality of rolling stands providing with a pair of caliber rolls 11 are arranged continuously and applying stretch reduction with a stretch reducer or a sizer. At this time, by installing a bulge width measuring device in the position of the outlet side of at least one stand of the mandrel mill and respectively and separately measuring the amount BL of left fin flows and the amount BR of right fin-flows which are distances from the center position of the hollow tube stock to the outside positions of the fin-flow parts on both sides, the difference ΔB between them is calculated. The tubes are managed as acceptable products when the obtained difference is within a predetermined value and as rejected products in the case other than that.