There is provided a magnetic tape, to be used at a running speed of at least 4,000 mm/sec., wherein servo signals for controlling tracking are recorded on the magnetic layer or the backcoat layer, and wherein the difference between the recording track width and the reproducing track width is 16 .mu.m or less, characterized in that the value of [.alpha./(Tw-Tr)] is 0.2 or less, wherein a [.mu.m] is an amount of a weave occurring on one of both edges of the magnetic tape and on the side of reference for the running of the tape; Tw [.mu.m] is a recording track width; and Tr [.mu.m] is a reproducing track width; and that a coefficient of humidity expansion in the tape widthwise direction is (0 to 14).times.10.sup.-6/% RH; and a coefficient of thermal expansion in the tape widthwise direction is (0 to 10).times.10.sup.-6/.degree. C. This magnetic tape has a recording track width of 28 .mu.m or less, and is excellent in servo performance, since a decrease in reproduction output due to off-track hardly occurs even when the difference between the recording track width and the reproducing track width is 16 .mu.m or less.