The concept of classification of organisms in Biology seems to pose a problem to Secondary School students in Kenya. Though, the topic is important for understanding of the basic elements of the subject. The Examinations Council in Kenya has identified teacher centred pedagogical techniques as one of the main causes for this. Project based learning technique has been successfully used as an instructional technique in countries like Japan and United States of America to improve students' academic achievement and positive attitude development among students in science practicals in Biology. The study therefore investigated the influence of project based learning technique on achievement of students in classification of organisms among Secondary Schools in Kenya with particular focus on academic achievement and attitude development. Quasi experimental design was employed. Stratified random sampling technique was used to select eight classes from four secondary schools with a total of 360 students. Students' Attitude Questionnaires and Classification Achievement Test were used as instruments. Analysis of Variance and t-test were employed in data analysis. The study revealed that project based learning technique enabled students to improve in academic achievement as well as developing positive attitude towards classification of organisms. The study recommends to the Ministry of Education and its agencies to adopt project based learning technique among other student centred instructional techniques for teaching of practical oriented concepts like Classification of Organisms.