A typical 1 cup sliced serving of cucumber contains 0.7 grams of protein (0.65 g per 100 g), which makes it only a minor source of protein. That covers roughly 1% of the 50 g reference Daily Value, so it adds toward your protein total for the day.
Around 17% of the calories in cucumber come from protein, so it is more of an energy food than a protein food. It contributes to a day's protein total, but the bulk of what it delivers is energy rather than amino acids - treat it as a contributor alongside a denser source, not as the protein in a meal.
Among the 105 vegetables in the database, cucumber ranks 88th by protein per serving, and 759th out of all 796 foods on the site. Set against cooked carrots, another vegetable entry in the database, a serving carries about 0.5 g less protein (cooked carrots has 1.2 g per 1 cup sliced).
It is an incomplete protein on its own; pairing it with other plant foods across the day covers the full range of essential amino acids. The serving above is measured by volume at 104 g. The per-100 g figure lets you compare it directly against any other food here, whatever its serving.
Source: USDA FoodData Central #168409 - "Cucumber, with peel, raw" (SR Legacy, published 4/1/2019). Values are the published reference figures for that record, not lab measurements for a specific brand or batch.
Quick answers
Cucumber protein FAQ
How much protein is in cucumber per 100 g?
Cucumber has 0.65 g of protein per 100 g. A typical 1 cup sliced serving (104 g) provides 0.7 g.
Is cucumber a complete protein?
No. Cucumber is an incomplete protein on its own; pairing it with other protein sources across the day covers the full range of essential amino acids.
How much of the Daily Value does a serving of cucumber cover?
A 1 cup sliced serving of cucumber contains 0.7 g of protein, about 1% of the 50 g reference Daily Value.
Is cucumber a good source of protein?
Cucumber is only a minor source of protein, and about 17% of its calories come from protein, which makes it more of an energy food than a protein food. Set against cooked carrots, another vegetable entry in the database, a serving carries about 0.5 g less protein (cooked carrots has 1.2 g per 1 cup sliced).