Red emitting phosphors KLa0.7-x(MoO4)2:0.3Eu3+, xSm3+ were synthesized by a solid-state reaction. Analysis on XRD patterns confirms that all the obtained phosphors exhibit pure phase. The luminescence properties and energy transfer behavior were studied via fluorescence spectral measurements. When the Sm3+ concentration is lower, the emission intensities under 277 and 394 nm excitations almost do not change with Sm3+ concentration, but effective luminescent enhancement is discovered in the samples with lower Sm3+ concentrations by 404 nm. However, Sm3+ doping quenches the emission of Eu3+ when the Sm3+ doping concentration is higher. The electric multipole interaction and exchange interaction models were adopted to explore physical nature for the energy transfer mechanism, and the exchange interaction between Sm3+ and Eu3+ is confirmed to be the right mechanism. It is found from the fluorescence decays that Sm3+ is the donor when the Sm3+ concentration is lower, but the Sm3+ doping quenches the luminescence of Eu3+ when the Sm3+ concentration is higher