diff --git a/NEWS.md b/NEWS.md
index 0fd950dcf6..3e92547b2a 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -9,6 +9,7 @@
 
 
 * Allow `stat` in `geom_hline`, `geom_vline`, and `geom_abline`. (@sierrajohnson, #6559)
+* `stat_boxplot()` treats `width` as an optional aesthetic (@Yunuuuu, #6575)
 
 # ggplot2 4.0.0
 
diff --git a/R/stat-boxplot.R b/R/stat-boxplot.R
index ff51b8354d..17635cd35b 100644
--- a/R/stat-boxplot.R
+++ b/R/stat-boxplot.R
@@ -5,6 +5,7 @@
 StatBoxplot <- ggproto("StatBoxplot", Stat,
   required_aes = c("y|x"),
   non_missing_aes = "weight",
+  optional_aes = "width",
   # either the x or y aesthetic will get dropped during
   # statistical transformation, depending on the orientation
   dropped_aes = c("x", "y", "weight"),
@@ -69,9 +70,11 @@ StatBoxplot <- ggproto("StatBoxplot", Stat,
     if (any(outliers)) {
       stats[c(1, 5)] <- range(c(stats[2:4], data$y[!outliers]), na.rm = TRUE)
     }
-
-    if (vec_unique_count(data$x) > 1)
+    if (length(data$width) > 0L) {
+      width <- data$width[1L]
+    } else if (vec_unique_count(data$x) > 1) {
       width <- diff(range(data$x)) * 0.9
+    }
 
     df <- data_frame0(!!!as.list(stats))
     df$outliers <- list(data$y[outliers])