Stripe order in La2-xSrxNiO4 with 0.289≲x≲1/2 was studied with the neutron-diffraction technique. The stripe order of holes and spins was observed at low temperatures in all samples. The incommensurability ε of the stripe order is approximately linear with the hole concentration nh up to x=1/2. We found that the stripe is most stable at nh=1/3 with ε=1/3 from the analyses of the onset temperatures of the charge and spin orderings and the nh dependence of the correlation length of the stripe order. The stability of an ε=1/3 stripe induces a systematic deviation of ε from the ε=nh law for samples with nh≠=1/3. This deviation affects the stripe order on both sides of the hole concentration with nh<1/3 as well as nh>1/3.