The quantum rotor is shown to be supersymmetric. The supercharge Q, whose square equals the Hamiltonian, is constructed with reflection operators. The conserved quantities that commute with Q form the algebra so(3) −1 , an anticommutator version of so(3). The subduced representation of so(3) −1 on the space of spherical harmonics with total angular momentum j is constructed and found to decompose into two irreducible components. Two natural bases for the irreducible representation spaces of so(3) −1 are introduced and their overlap coefficients prove expressible in terms of orthogonal polynomials of a discrete variable called anti-Krawtchouk polynomials.This paper is cordially dedicated to Mourad Ismail on the occasion of his 70 th birthday.