The purpose of this study is to confirm the characteristics of the sentence including “yoku” with the meaning of evaluation and to confirm the semantic characteristics based on that for the concrete consideration.The advanced research showed that there are at least two meanings in “yoku”. However, I could not find any research to determine about the reason why there are at least two meanings in that case and the detailed characteristics of the sentence that will be shown in my research. Firstly, as the way of the research, when an example was collected from the same conditions, I considered the percentage of the evaluative usage and the distinguishing characteristics different from the usage to measure the frequency or the quantity. The result was that the proportion of the evaluative usage was under 10% out of all the samples, and I could confirm that they have been used in the colloquial literature in most cases.And I analyzed the samples with the 5 criteria. As a result, I could find that there is a tendency to come first in the sentence when “yoku” has the meaning of evaluation, and when it is cataphoric, the usage was always evaluation usage and frequently used together with benefactive expression or possibility expression. And in most cases, it was used only in the affirmative sentence.Categorizing by the meaning, “yoku” appears when all the propositions are different from the speaker’s expectation. Eventually it can be said that they have same internal structure and the characteristic of “yoku” is to show the speaker’s evaluation on when a proposition which is differ from the expectation comes true. It can be also said that the criteria of the evaluation is in the consciousness of the speaker and as the evaluation itself is a decision by the speaker so “yoku” with the meaning of evaluation appears in the colloquial literature in most cases.