The purposes of this research are to investigate the effects of problem-based learning on 1) students’ achievement 2) skills of mathematical problem solving in daily life 3) attitude toward Mathematics learning of students in Prathom Suksa two. The research sample is 68 students in Prathom Suksa two of Chulalongkorn University Demonstration Elementary School, divided into 2 groups: 34 students in the experimental group and 34 students in control group. This research was conducted for 9 weeks. The instruments used in this research are following. 1) The achievement test of Mathematics learning is fill-in-the-blank objective test scoring 1 point for correct answer and 0 point for incorrect answer. The test difficulty index and discrimination index ranges 0.38 to 0.75 and 0.25 to 0.75 respectively, with its average reliability index is 0.72. 2) The test of mathematical problem solving skill in daily life is fill-in-the-blank objective test divided in 6 parts and scores according to the provided rubric. And, 3) the test of attitude toward Mathematics learning in daily life is a 5-rating scale composed of positive and negative questions about intelligence, feeling, and behavior with 0.80 of average reliability index. The data were analyzed by using descriptive statistics with mean standard Deviation and independent sample t-test of experimental and control group. The qualitative data were collected with classroom observation and analyzed with content analysis. The results of the effects of problem-based learning on the students’ achievement, and skills of mathematical problem solving in daily life, as well as attitude toward Mathematics learning of students in Prathom Suksa two were concluded as following: 1. The mean scores of the students’ achievement and the skills of mathematical problem solving in daily life of both experimental and control group were statistically significant differences as p < 0.05. 2. The mean scores of the attitude toward Mathematics were on average level but no statistically significant difference between experimental and control group.