This paper studies a kind of minimal time control problems related to the exact synchronization for a controlled linear system of parabolic equations. Each problem depends on two parameters: the bound of controls and the initial state. The purpose of such a problem is to find a control (from a constraint set) synchronizing components of the corresponding solution vector for the controlled system in the shortest time. In this paper, we build up a necessary and sufficient condition for the optimal time and the optimal control; we also obtain how the existence of optimal controls depends on the above mentioned two parameters.2010 Mathematics Subject Classifications. 49K20, 93B05, 93B07, 93C20 y(t; y 0 , u) = (y 1 (t; y 0 , u), y 2 (t; y 0 , u), . . . , y n (t; y 0 , u)) ⊤ for the solution of the system (1.1). (Here and throughout this paper, we denote the transposition of a matrix J by J ⊤ .) It is well known that for each T > 0, y(·; y 0 , u) ∈ W 1,2 (0, T ; H −1 (Ω) n ) ∩ L 2 (0, T ; H 1 0 (Ω) n ) ⊆ C([0, T ]; L 2 (Ω) n ). We will treat this solution as a function from [0, +∞) to L 2 (Ω) n .We next define control constraint set U M (with M > 0) and the target set S as follows:S {(y 1 , y 2 , . . . , y n ) ⊤ ∈ L 2 (Ω) n : y 1 = y 2 = · · · = y n }.Given M > 0, y 0 ∈ L 2 (Ω) n , we define the minimal time control problem (T P ) y 0 M :T (M, y 0 ) inf u∈U M {T ≥ 0 : u(·) = 0 and y(·; y 0 , u) ∈ S over [T, +∞)}.About Problem (T P ) y 0 M , several notes are given in order: (a 1 ) We call T (M, y 0 ) the optimal time; we call u ∈ U M an admissible control if there is T ≥ 0 so that u(·) = 0 and y(·; y 0 , u) ∈ S over [T, +∞); we call u * ∈ U M an optimal control if T (M, y 0 ) < +∞, u * (·) = 0 and y(·; y 0 , u * ) ∈ S over [T (M, y 0 ), +∞); we agree that T (M, y 0 ) = +∞ if the problem (T P ) y 0 M has no admissible control.(a 2 ) One can easily check that if y = (y 1 , y 2 , . . . , y n ) ⊤ ∈ L 2 (Ω) n , then y ∈ S if and only if Dy = 0, where and throughout this paper,