PURPOSE:To improve a collapsing property by dissolving phosphate, etc. in a urea-modified phenolic resin obtained by cocondensation of phenols, urea and formaldehyde thereby allowing molds after casting to collapse by mechanical impact alone. CONSTITUTION:About 3-30pts.wt. >=1 kind among phosphate, phosphite, phosphonate and phosphines are dissolved in 100pts.wt. urea-modified phenolic resin obtd. by cocondensation by using 1.0mol phenols, 0.1-1.0mol urea, and 0.6-1.2 mol formaldehyde, whereby a resin compsn. for shell molds is obtd. The molds which are produced by using the coated sand coated with such resin compsn. and hexamethylene tetramine at about 100-200 deg.C and are used mainly for casting of relatively low casting temps. such as Al castings collapse easily by mechanical impact alone withtout heat treatments after casting.