The present invention provides thermostable phospholipase TA3 and TA13 which are mutants of phospholipase A1 involving the hydrolysis/synthesis of phospholipids, the mutated genes encoding the same, microorganisms transformed with recombinant expression vectors comprising the mutated genes and a process for preparing phospholipase A1 mutants therefrom. The process for preparing phospholipase A1 mutant of the invention comprises the steps of: culturing E. coli strain transformed with a recombinant expression vector comprising a gene coding for phospholipase A1 mutant derived from Serratia sp.; and, isolating and purifying phospholipase A1 mutant from the culture. Since phospholipase A1 mutants of the invention have been improved in terms of thermal stability and enzyme activity as well, they can be practically applied to various biological process, pharmaceutics, cosmetics and food industries.