We recently created a unique gain-of-function mouse model with Sertoli cell-specific transgenic androgen receptor expression (TgSCAR) that showed SCAR activity controls the synchronized postnatal development of somatic Sertoli and Leydig cells, and meiotic-postmeiotic germ cells. Moderate TgSCAR (TgSCAR^m) expression reduced testis size but had no effect on male fertility. Here, we reveal that higher TgSCAR expression (TgSCAR^H) causes male infertility. Higher SCAR activity, shown by upregulated AR-dependent transcripts (Rhox5, Spinw1), resulted in smaller adult TgSCAR^H testes (50% of normal), despite normal or elevated circulating and intratesticular testosterone levels. Unlike fertile TgSCAR^m males, testes of adult TgSCAR^H males exhibited focal regions of interstitial hypertrophy featuring immature adult Leydig cells, and higher intratesticular dihydrotestosterone and 5α-androstane 3α, 17β-diol levels which are normally associated with pubertal development. Mature TgSCAR^H testes also exhibited markedly reduced Sertoli cell numbers (70%), although meiotic and postmeiotic germ cell to Sertoli cell ratios were 2-fold higher than normal, suggesting elevated TgSCAR activity supports excessive spermatogenic development. Concurrent with the higher germ cell load of TgSCAR^H Sertoli cells were increased levels of apoptotic germ cells in TgSCAR^H relative to TgSCAR^m testes. In addition, TgSCAR^H testes displayed unique morphological degeneration that featured accumulated cellular and spermatozoa clusters in dilated channels of rete testes, consistent with reduced epididymal sperm numbers. Our findings reveal for the first time that excessive Sertoli cell AR activity in mature testes can reach a level that disturbs Sertoli-germ cell homeostasis, impacts focal Leydig cell function, reduces sperm output and disrupts male fertility.