The form of the first movements of Mozart's Concerto for T재 pianos andOrchestra, K.242(1776) and Concerto for Three Pianos and Orchestra, K.365(1779)is the topic of this paper, from the point of views of Johann Christian Bach'sConcerto for Harpsichord and Orchestra, Op. 7 as a model and of Robert Levin'sformal skim of Mozart's mature piano concertos.Among concertos composed in Salzburg during the same years, there is no significant difference in formal organization. The double and triple concerto havesome common features. The concertos are based on the three-tutti from: opening,middle, and final. The layout of thematic materials is very systematic--regular use of sujet libre is a notable feature. The placement of half-cadence(in the tonic anddominant) is rather regular and important. The duplication or proliferation of the closing material are found. The formal organizations of the first movements of these two concertos follow not only Mozart's model concertos, J. C. Bach's Op. 7,but match well with Levin's formal skim of Mozart;s mature solo piano concertos.