Weibo is an increasingly popular form of social media and accumulates vast amounts of information making the measurement of social mood easily. The paper is about how to measure public mood using Weibo directly and efficiently. We proceed in three phases to measure and validate the social mood on Weibo. In the first phase, we create the Weibo Five Basic Mood Lexicon (Weibo-5BML). In perspective of emotional categorical approach, there are five basic emotions including Happiness, Sadness, Fear, Anger and Disgust. We collect emotional words as many as possible and ask three psychological graduates to judge every word belong to which kind of basic emotion discretely. At last, we get the formal version of the Weibo-5BML. There are 818 emotional terms in the Weibo-5BML, in which Happiness has 306 terms, Sadness has 205 terms, Fear has 72 terms, Anger has 93 terms, and Disgust has 142 terms. In the second phase, we generate social mood time series. We crawl and analyze minute texts in Sina Weibo using a transparent approach named term-based matching technique, which matches the emotional terms used in each tweet against Weibo-5BML. The Weibo-5BML could capture a variety of naturally occurring emotional terms in Weibo tweets and map them to their respective social mood dimensions. The score of each basic mood dimension is thus determined as the sum of each tweet term that matched the Weibo-5BML each day. Then we obtain five basic social moods daily series from July 1, 2011 to November 30, 2012. In the third phase, we validate the Weibo social moods by different kind of methods. First, we calculate the frequency of each social mood and find the frequency of happiness is higher than other four social moods which correspond to the relevant researches of people expressing happiness more and the hyperpersonal interaction model. Second, we calculate the correlation of five social moods and the result is consistent with the circumplex model of emotion. Happiness is negative correlation with the other four kind of social moods, while the four kinds of social moods are positive correlation with each other. Third, we get the fluctuation of five social moods during a week and the result is similar with other relevant researches. People are happier on weekends than workdays and the unhappiest day is Wednesday. At last, we match the five basic Weibo social moods against the fluctuations recorded by major events of social and popular culture and find these events cause corresponding fluctuation in Weibo social moods. Such as people are happy on both Chinese and Western holiday and the public is angry because of the conflict of Diaoyu Island. People are sad about the fragile life and the dead or injured passengers at the beginning of “7.23 Wenzhou Train Collision”, while angry at the fourth and fifth day because of the cause tracing. All of these results indicate that the social mood on Weibo is effective on capturing the public’s mood. It is useful for combining the psychological theory and techniques of computing science and these text and image information on Internet provide the valuable resources and opportunities for researchers to study the individual or collective characteristics.