A　new　chiral　sulfide　family,　Ln(4)InSbS(9)　(Ln　=　La,　Pr,　Nd),　with　its　own　structure　type　in　space　group　P4(1)2(1)2　or　its　enantiomorph　P4(3)2(1)2　has　been　synthesized　by　solid-state　reaction.　Remarkably,　the　La　member　shows　the　strongest　Kleinman-forbidden　second　harmonic　generation　to　date,　with　an　intensity　1.5　times　that　of　commercial　AgGaS2　at　a　laser　wavelength　of　2.05　mu　m,　and　exhibits　type-I　phase-matchable　behavior.　Density　functional　theory　calculations　and　ab　initio　molecular　dynamics　simulations　suggest　that　lattice　vibrations　may　be　responsible　for　the　origin　and　magnitude　of　the　strong　SHG　effect.