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Different factors, including antimicrobial resistance, may diminish the effectiveness of antibiotic therapy, challenging the management of post-transplant urinary tract infection (UTI). The association of acidic urine pH with microbiological and clinical outcomes was evaluated after fosfomycin or ciprofloxacin therapy in 184 kidney transplant recipients (KTRs) with UTI episodes by <i>Escherichia coli</i> (N = 115) and <i>Klebsiella pneumoniae</i> (N = 69). Initial urine pH, antimicrobial therapy, and clinical and microbiological outcomes, and one- and six-month follow-up were assessed. Fosfomycin was prescribed in 88 (76.5%) <i>E. coli</i> and 46 (66.7%) <i>K. pneumoniae</i> UTI episodes in the total cohort. When the urine pH ≤ 6, fosfomycin was prescribed in 60 (52.2%) <i>E. coli</i> and 29 (42.0%) <i>K. pneumoniae</i>. Initial urine pH ≤ 6 in <i>E. coli</i> UTI was associated with symptomatic episodes (8/60 vs. 0/55, <i>p</i> = 0.04) at one-month follow-up, with a similar trend in those patients receiving fosfomycin (7/47 vs. 0/41, <i>p</i> = 0.09). Acidic urine pH was not associated with microbiological or clinical cure in <i>K. pneumoniae</i> UTI. At pH 5, the ciprofloxacin MIC₉₀ increased from 8 to >8 mg/L in <i>E. coli</i> and from 4 to >8 mg/L in <i>K. pneumoniae</i>. At pH 5, the fosfomycin MIC₉₀ decreased from 8 to 4 mg/L in <i>E. coli</i> and from 512 to 128 mg/L in <i>K. pneumoniae</i>. Acidic urine is not associated with the microbiological efficacy of fosfomycin and ciprofloxacin in KTRs with UTI, but it is associated with symptomatic UTI episodes at one-month follow-up in <i>E. coli</i> episodes.