Learning application are applications developed for learning purpose using mobile technologies to enhance students learning. However, in spite of the rapid use of mobile devices among undergraduates in Nigerian Universities, many students use mobile devices for unproductive activities. Hence, this study therefore, focused on the effectiveness of Chemistry Learning-App for Nigerian Undergraduates in a Blended Learning Environment. The objectives of this study was to (i) determined experts’ rating of the developed Chemistry Learning-App;(ii) examined the effectiveness of the Chemistry Learning-App on undergraduates’ academic performance in a blended learning environment and those taught with conventional lecture method; (iii) examined the influence of gender on academic performance of undergraduates exposed to Chemistry Learning-App in blended learning environment. The research instruments used were; Chemistry Learning-App, Students’ Academic Performance Test and Experts Rating of the Chemistry Learning-App with the reliability value of .71. This study used quasi pretest posttest of non-equivalent experimental design. A total of 60 undergraduates were sampled for the study. The study concluded that undergraduates exposed to Chemistry Learning-App performed better than their counterpart taught using conventional lecture method. The implication is that Chemistry academic performance of undergraduates would improve if students are exposed to the developed Leaning-App. It was recommended among others that undergraduates should complement instruction with the use of the developed Learning-App.