A flame-retardant, characterized in that it comprises a layered titanic acid in the form of a nano sheet which is formed by a method comprising treating a layered titanic acid salt with an acid or warm water and then reacting the resultant mixture with an organic basic compound, or carrying out the step of treating a layered titanic acid salt with an acid or warm water and the step of reacting with an organic basic compound, in one pot, to thereby swell or separate the layers; and a flame-retardant resin composition, characterized in that it comprises 100 parts by weight of a resin and 0.5 to 50 parts by weight of the above layered titanic acid in the form of a nano sheet.