Abstract: An anti-derailing device for a sliding door, including slide rollers on upper edges of two sides of the sliding door, anti-bounce rollers below the slide rollers, rail supporting bases on a fixed door in front of the sliding door, and a rail fixed on opposite outer sides of the sliding door and the fixed door and clamped between the rollers. Each roller includes a fixed part and a first adjusting part which includes a first eccentric roller combined with the fixed part, each roller includes a fixing part and a second adjusting part which includes a second eccentric roller combined with the fixing part, and each rail supporting base includes a positioning part and a holding part for holding the rail. By adjusting positions of the rollers and without pre-machined holes, the sliding door can operate balanced and smoothly and prevent the rail from derailing.