This paper describes a method for the expansion of the size of texts using an efficient string replacement algorithm. A method for the expansion of the size of texts by use of morpheme replacements is supported by the rules for expansion morphemes. This paper explains the text expansion method using the example of text reduction. Morpheme replacements are defined as a combination of a pattern of categories and restrictions on morphemes. A replaceable pattern is efficiently detected through an extension of Aho's string pattern-matching algorithm. This extension consists of the application of a matching algorithm that replaces the input morpheme. Results of simulations upon several texts show that reduced texts are between 5% and 10% shorter than their original counterparts. Also, by use of this pattern-matching algorithm for detection of the suitable reducing rules, the number of state translations can be reduced to 1 7 of that when using Aho's pattern-matching algorithm.