The incorporation of Sn into LaMnO₃ perovskite and its influence on magnetotransport properties were studied in samples synthesized at low temperature. Single-phase materials for two series of samples with La/(Sn+Mn)=1 and La/(Sn+Mn) < 1 ratios were obtained by substitution of up to 10% of the Mn ions by Sn⁴⁺. The effect of Sn substitution was monitored through measurements of thermal, M(T), and magnetic field, M(H), dependences of magnetization, as well as of resistivity, ρ(T), at 0 and 70 kOe. These showed that this effect depends strongly on the perovskite cation site ratio (A/B). For La/(Sn+Mn)=1, M and T_C were depressed as Sn content was increased. The magnetization data suggest the presence of magnetic clusters with superparamagnetic behavior. No evidence of magnetoresistance (MR) was found. For La/(Sn+Mn) < 1 ratio, the samples showed ferromagnetic behavior and MR and both M and T_C raised as Sn content increased. The results are discussed in terms of A site vacancies.