The effects of line tying on resistive tearing instability in slab geometry are studied within the framework of reduced magnetohydrodynamics [B. B. Kadomtsev and O. P. Pogutse, Sov. Phys. JETP 38, 283 (1974); H. R. Strauss, Phys. Fluids 19, 134 (1976)]. It is found that line tying has a stabilizing effect. The tearing mode is stabilized when the system length L is shorter than a critical length Lc, which is independent of the resistivity η. When L is not too much longer than Lc, the growth rate γ is proportional to η. When L is sufficiently long, the tearing mode scaling γ∼η3/5 is recovered. The transition from γ∼η to γ∼η3/5 occurs at a transition length Lt∼η−2/5.