Abstract : Alpha particle condensation is studied in 12C and 16O with the orthogonality condition model (OCM). The OCM equation is an approximation of the equation of motion of α bosons based on microscopic theories. We demonstrate that 1) the Hoyle state (the 0+2 state at 7.65 MeV in 12C), located just above the 3α disintegration threshold has a 3α-particle condensate character, in which 3α particles occupy an identical 0S orbit with 70 % occupancy, forming a dilute gas-like configuration, and 2) the 0+6 state at Ex = 15.1 MeV in 16O, appearing above the 4α breakup threshold, is a strong candidate with dilute 4α structure of the condensate-type.