Aprobabilitydensityfunction(PDF)isderivedofbetadistributionwithbothλ3(skewness)andλ4(kurtosis)asparametersforweaklynonlinearwavesurfaceelevationbyuseofamethodrecentlyproposedbySrokosz.ThisPDFnotonlyhasasimplerformthanthewell-knownGram-CharlierSeriesPDFderivedbyLonguet-Higgins,butalsoovercomesanobviousshortcomingofthelatterthatwhentheseriesisunsuitablytruncated,theresultingPDFislocallynegative.TotestthederivedbetaPDF,laboratorialexperimentsofwindwavesareconducted.TheexperimentaldataindicatethatthetheoreticalrequirementsoftheparametersinthebetaPDFarefulfilled.TheexperimentalresultsshowthatthepresentPDFisinbetteragreementwiththemeasureddatathanthebetaPDFonlyincludingparameterλ3,andalsothantheGram-CharlierSeriesPDFtruncateduptothetermofH6.