BACKGROUND:　Almonds　contain　considerable　amounts　of　potential　prebiotic　components,　and　the　roasting　process　may　alter　these　components.　The　aim　of　this　study　was　to　compare　the　in　vitro　fermentation　properties　and　in　vivo　prebiotic　effect　of　raw　and　roasted　almonds.　RESULTS:　In　vitro,　predigested　raw　and　roasted　almonds　promoted　the　growth　of　Lactobacillus　acidophilus　(La-14)　and　Bifidobacterium　breve　(JCM　1192),　and　no　significant　differences　were　found　between　these　two　nuts.　In　a　4-week　animal　trial,　daily　intake　of　raw　or　roasted　almonds　promoted　the　population　of　Bifidobacterium　spp.　and　Lactobacillus　spp.　and　inhibited　the　growth　of　Enterococcus　spp.　in　faeces　and　caecal　contains　of　rats.　Compared　with　roasted　almonds,　raw　almonds　had　a　greater　bifidobacteria　promotion　effect.　Besides,　significantly　higher　beta-galactosidase　activity　and　lower　beta-glucuronidase　and　azoreductase　activities　in　faeces　or　caecal　contents　of　rats　were　observed　with　raw　almonds　than　with　roasted　almonds.　While,　in　terms　of　metabolic　effects,　the　ingestion　of　roasted　almonds　resulted　in　significantly　greater　intestinal　lipase　activities.　CONCLUSION:　Both　raw　and　roasted　almonds　exhibit　potential　prebiotic　effects,　including　regulation　of　intestinal　bacteria　and　improved　metabolic　activities.　The　roasting　process　may　slightly　reduce　the　prebiotic　effects　of　almonds　but　significantly　improve　the　metabolic　effects.　(C)　2016　The　Authors.　Journal　of　the　Science　of　Food　and　Agriculture　published　by　John　Wiley　&　Sons　Ltd　on　behalf　of　Society　of　Chemical　Industry.